DataPDF Available


ACMG StAteMent
© American College of Medical Genetics and Genomics
American College of Medical Genetics and Genomics (ACMG)
guidelines and statements have assisted patients seeking pre-
natal screening information and health-care providers respon-
sible for providing accurate and up-to-date information to their
patients.1–3 Until recently, noninvasive prenatal screening for
aneuploidy relied on measurements of maternal serum ana-
lytes and/or ultrasonography. ese have a false-positive rate of
approximately 5% and detection rates of 50–95%, depending on
the specic screening strategy used. Advances in genomic tech-
nologies led to noninvasive prenatal screening that relies on the
presence of cell-free DNA derived from the placenta but cir-
culating in maternal blood, which is referred to here as nonin-
vasive prenatal screening (NIPS). Massive parallel sequencing
of maternal and placental (also called fetal when speaking of
the fraction of this DNA in maternal blood) fragments of DNA
occurs simultaneously. Sequencing with quantication can be
random, targeted, and followed by quantication or exploi-
tation of single-nucleotide polymorphisms.4–8 Alternatively,
sequencing can take place by measuring the release of hydrogen
ions as nucleotides are added to a DNA template (i.e., semicon-
ductor sequencing).9 Microarray technology can also be used
to quantify DNA.10 Bioinformatics that enable these method-
ologies is complex and proprietary. Since the introduction of
NIPS in 2011, health-care providers and patients have experi-
enced marketing pressures, rapidly evolving professional prac-
tice guidelines, and confusion regarding the appropriate role of
Submitted 7 June 2016; accepted 7 June 2016; advance online publication 28 July 2016. doi:10.1038/gim.2016.97
Genet Med
Genetics in Medicine
ACMG Statement
© American College of Medical Genetics and Genomics
Noninvasive prenatal screening using cell-free DNA (NIPS) has been
rapidly integrated into prenatal care since the initial American Col-
lege of Medical Genetics and Genomics (ACMG) statement in 2013.
New evidence strongly suggests that NIPS can replace conventional
screening for Patau, Edwards, and Down syndromes across the
maternal age spectrum, for a continuum of gestational age beginning
at 9–10 weeks, and for patients who are not signicantly obese. is
statement sets forth a new framework for NIPS that is supported by
information from validation and clinical utility studies. Pretest coun-
seling for NIPS remains crucial; however, it needs to go beyond dis-
cussions of Patau, Edwards, and Down syndromes. e use of NIPS
to include sex chromosome aneuploidy screening and screening for
selected copy-number variants (CNVs) is becoming commonplace
because there are no other screening options to identify these con-
ditions. Providers should have a more thorough understanding of
patient preferences and be able to educate about the current draw-
backs of NIPS across the prenatal screening spectrum. Laboratories
are encouraged to meet the needs of providers and their patients by
delivering meaningful screening reports and to engage in education.
With health-care-provider guidance, the patient should be able to
make an educated decision about the current use of NIPS and the
ramications of a positive, negative, or no-call result.
Genet Med advance online publication 28 July 2016
Key Words: cell-free fetal DNA; noninvasive prenatal testing;
prenatal genetic screening
1Department of Obstetrics and Gynecology, University of Florida, Gainesville, Florida, USA; 2Department of Pediatrics, Harvard Medical School and Division of Medical Genetics,
Department of Pediatrics, Massachusetts General Hospital, Boston, Massachusetts, USA; 3American College of Medical Genetics and Genomics, Bethesda, Maryland, USA; 4GeneDx,
Gaithersburg, Maryland, USA; 5New York City Health + Hospitals/Albert Einstein College of Medicine, Bronx, New York, USA; 6University of South Carolina School of Medicine,
Greenville Health System, Greenville, South Carolina, USA; 7Montefiore Medical Center, Department of Obstetrics & Gynecology and Women’s Health, Albert Einstein College of
Medicine, Bronx, New York, USA. Correspondence: Anthony R. Gregg (
The Board of Directors of the American College of Medical Genetics and Genomics approved this statement on 23 May 2016.
Noninvasive prenatal screening for fetal aneuploidy,
2016 update: a position statement of the American College
of Medical Genetics and Genomics
AnthonyR.Gregg, MD, MBA1, BrianG.Skotko,MD, MPP2, JudithL.Benkendorf,MS3,
KristinG.Monaghan,PhD4, KomalBajaj,MD5, RobertG.Best,PhD6, SusanKlugman,MD7 and
MichaelS.Watson,MS, PhD3; on behalf of the ACMG Noninvasive Prenatal Screening Work Group
Disclaimer: is statement is designed primarily as an educational resource for clinicians to help them provide quality medical services. Adherence to this statement
is completely voluntary and does not necessarily assure a successful medical outcome. is statement should not be considered inclusive of all proper procedures and
tests or exclusive of other procedures and tests that are reasonably directed toward obtaining the same results. In determining the propriety of any specic procedure
or test, the clinician should apply his or her own professional judgment to the specic clinical circumstances presented by the individual patient or specimen.
Clinicians are encouraged to document the reasons for the use of a particular procedure or test, whether or not it is in conformance with this statement. Clinicians
also are advised to take notice of the date this statement was adopted and to consider other medical and scientic information that becomes available aer that date.
Italso would be prudent to consider whether intellectual property interests may restrict the performance of certain tests and other procedures.
Volume 18 | Number 10 | October 2016 | GENETICS in MEDICINE
Noninvasive prenatal screening for fetal aneuploidy: 2016 update | GREGG et al ACMG StAteMent
NIPS in prenatal practice.11–15 is position statement replaces
the 2013 “ACMG Statement on Noninvasive Prenatal Screening
for Fetal Aneuploidy.”3
We emphasize that all genetic screening has residual risk (i.e.,
risk of having a genetic condition even aer receiving a negative
or “normal” result). is concept is independent of the screen-
ing modality, condition screened, or number of conditions
screened. e concept of residual risk supports our use of the
acronym NIPS, where the “S” represents screening. It is impor-
tant to emphasize what NIPS does not provide to patients. NIPS
is not used clinically to screen for single-gene disorders (e.g.,
variation in the genome caused by relatively small changes in
nucleotide sequence). NIPS is not used to predict late preg-
nancy complications. NIPS does not screen for open neural
tube defects; therefore, maternal serum α-fetoprotein testing
to screen for open neural tube defects should still be oered at
15–20 weeks of gestation. NIPS does not replace routine fetal
anatomic screening using ultrasound.
Screening tests move through a predictable stepwise progres-
sion from laboratory development to clinical use. e ACMG
recognizes this course as (i) analytical validity, (ii) clinical valid-
ity, and (iii) clinical utility. e last of these is the most complex.
• Analytical validity refers to whether the screening test
detects the target of the test in those with the target (ana-
lytical sensitivity) without detecting it in those without
the target (analytical specicity). Regarding NIPS, ana-
lytical validity asks whether various concentrations of
maternal and placental DNA can be used to determine
the presence or absence of fetal aneuploidy (or other
conditions). Analytical validity has been established
for the variety of screening methods discussed in this
• Clinical validity refers to how well NIPS performs and
focuses on detection rate (DR), the proportion of those
who screen positive and will have the clinical condi-
tion (clinical sensitivity), and the proportion who will
not (clinical specicity (SPEC)). ese test metrics are
independent of the prevalence of the condition being
screened. Because NIPS addresses fairly uncommon con-
ditions, validation studies are used to understand the DR
and SPEC using banked or research samples. is allows
overrepresentation of samples for the target condition of
interest. Between 2011 and 2013, there were at least eight
widely quoted validation studies spread across four labo-
ratories oering NIPS clinically.4–8,20–22 Validation studies
reached similar conclusions. NIPS had very high DR and
SPEC, reaching nearly 99% for Down syndrome caused
by trisomy 21, translocations, and trisomy 21 mosaicism.
e DR and SPEC were 80–100% for Edwards syndrome
caused by trisomy 18 and trisomy 18 mosaicism, as well
as for Patau syndrome caused by trisomy 13, transloca-
tions and trisomy 13 mosaicism. In this document, we
refer to all three syndromes as “traditionally screened
aneuploidies.” us, in clinical validation studies, NIPS
was shown to outperform conventional screening
• Clinical utility refers to whether a screening test is reli-
able and useful to patients. Clinical utility studies inform
patients, providers, and payers about decision making.
ese studies can provide objective test metrics such as
positive predictive values (PPVs) and negative predic-
tive values (NPVs). It is noteworthy that PPV and NPV
can be determined for a population by modeling (using
DR and SPEC as well as population prevalence) or by
actual measure. Furthermore, one can establish PPV on
a population basis (e.g., all women of a certain age) or
individually (using information that is patient-specic).
Cost ecacy in terms of dollars or cost utility measured
by cost per case detected or quality-adjusted life-year is
also used to describe clinical utility.26 Because cost e-
cacy and cost utility studies use a high degree of model-
ing and assumptions (clinical care and monetary), these
are at risk for bias (systematic and random). We chose
not to include studies of this nature when making our
Genetic testing and screening modalities used in pregnancy,
such as NIPS, are oered with the aim of providing patients
information that can help them optimize their pregnancy
outcomes.27 It is accepted practice, when implementing these
modalities, to follow a multifaceted process in which genetic
counseling is a common thread. Specic steps include: pretest
education, counseling, and informed consent; the screening
or testing procedure; a laboratory component that includes
test interpretation; and, nally, the disclosure of results to the
patient within a context that includes the appropriate educa-
tion, counseling, and follow-up.
e core of genetic counseling is establishing patient desire
and expectations. Genetic counseling is not merely educational;
it is a patient-centered form of medical communication facili-
tating decisions on a course of action that are made solely by
the patient once the patient has been given the necessary facts,
alternatives, and anticipated consequences.28,29 In this context,
genetic counseling follows the Rogerian method, which is cli-
ent-centered and nondirective.30 ACMG recognizes it is beyond
the scope of prenatal care providers to describe all genetic con-
ditions amenable to diagnosis or screening in a pretest counsel-
ing session. However, an eort should be made to discuss in a
general way the types of conditions that can (e.g., aneuploidy,
translocations, microdeletions, and microduplications) and
cannot (e.g., many single-gene disorders), be identied, includ-
ing test limits in the case of the former, when a family history is
GENETICS in MEDICINE | Volume 18 | Number 10 | October 2016
GREGG et al | Noninvasive prenatal screening for fetal aneuploidy: 2016 update
ACMG StAteMent
Patient preferences for information should play a pivotal role
in guiding the use of NIPS in prenatal care. is is in keeping
with generally accepted genetic counseling tenets and respects
that clinical utility may vary between patients.28,29 Clinical utility
includes test metrics (PPV and NPV), cost, and a patient’s unique
value system construct framed by (among other things) cultural
traditions and religious beliefs. We recognize that this construct
is not homogeneous across the United States. e desire for
diagnostic testing or screening, the uptake of diagnostic test-
ing, and decisions made when positive results are conrmed
are inuenced by a patient’s value system. However, establish-
ing a patient’s value system construct can be complex and con-
fusing. In the context of an evolving technology such as NIPS,
the patient’s ability to accept uncertainty with regard to possible
screening outcomes should also be considered and explored as
part of the pretest communication process. Cost plays a role in
society’s willingness to pay. Insurance coverage (private or pub-
lic), responsibility for co-payments, and out-of-pocket expenses
factor into the nature of follow-up diagnostic tests, availability of
genetic counseling services, and reproductive decision making.
For the genetic testing and screening modalities used in preg-
nancy to provide patients with information that can help them
optimize their pregnancy outcomes, patients must be allowed
to make informed choices that occur across a time continuum.
Prenatal screening and diagnostic testing target 20 weeks of ges-
tation as an upper limit for implementation.32 Decision making
is circumscribed by state-specic laws (e.g., 20 weeks),33 which
highlights the importance of timely delivery and processing
of accurate and complete information at each step. NIPS can
be performed at an earlier gestational age than conventional
screening, and there is no gestational age upper limit aer 10
weeks of gestation. is means that patients can get the most
accurate screening information at an earlier gestational age,
thus enhancing informed decision making.
• ACMG recommends:
○ Providing up-to-date, balanced, and accurate infor-
mation early in gestation to optimize patient decision
making, independent of the screening approach used.
○ Laboratories work with public health ocials, policy-
makers, and private payers to make NIPS, including
the pre- and posttest education and counseling, acces-
sible to all pregnant women.
For some patients the goal in prenatal screening may be
to maximize the detection of fetal genetic diagnoses. In this
scenario, fetal diagnostic testing (e.g., chorionic villous sam-
pling or amniocentesis) followed by chromosomal microarray
(CMA) using fetal DNA should be oered, and NIPS may not
be the best choice. With diagnostic testing, whole-chromosome
abnormalities, unbalanced chromosome rearrangements, small
losses or gains of chromosomal material (CNVs), and in some
cases single-gene disorders can be detected. An NIH study of
prenatal CMA suggested the background rate of small clinically
signicant CNVs is 1–2%.34 Fetal diagnostic testing carries a
small risk. Pregnancy loss rates before 24 weeks of gestation
for amniocentesis range from 0.1 to 0.9% (1/1,000–1/111) and
for chorionic villous sampling range from 0.2 to 1.3% (1/500–
1/77).35,36 Results from these studies reect diagnostic testing
performed because of abnormal ultrasound ndings, positive
aneuploidy screening, or other at-risk conditions. erefore,
one can conclude that these procedure-related miscarriages are
overestimates of risk compared to selecting a procedure solely
for obtaining maximal information.
Patients may prefer a screening test, and there are many to
choose from. Conventional screening approaches such as rst-
trimester screening, second-trimester screening, or combina-
tions of both (e.g., stepwise sequential screening) have good
detection rates (80–95%) but high false-positive rates (3–5%).
Stepwise sequential screening has both (~95% and ~5%) but
is not universally used due to the required logistics. When
choosing a conventional screening approach, patients should
be aware of the high false-positive rate, which may lead to diag-
nostic procedures and, consequently, diagnoses not detected
by NIPS (e.g., some chromosome abnormalities and CNVs).
For patients who prefer to avoid diagnostic testing but desire
highly accurate screening for Patau, Edwards, and Down syn-
dromes, NIPS may be preferred. ere are pros and cons to any
screening approach. Aer careful counseling, patients will ide-
ally select the paradigm that is most aligned with their goals.
Prenatal care providers should try to understand the clinical
utility construct of individual patients during the informed
consent and decision-making processes.
• ACMG recommends:
○ Allowing patients to select diagnostic or screening appro-
aches for the detection of fetal aneuploidy and/or genomic
changes that are consistent with their personal goals and
○ Informing all pregnant women that diagnostic testing
(CVS or amniocentesis) is an option for the detection
of chromosome abnormalities and clinically signicant
In 2013, the ACMG was careful not to restrict NIPS to spe-
cic patient groups.3 Recent clinical utility trials23–25,37 com-
pared NIPS to conventional screening methods for women at
low risk or average risk compared to women at high risk. e
DR, SPEC, PPV, and NPV for Patau, Edwards, and Down syn-
dromes were reported. Clinical utility, measured as PPV and
NPV in these studies, supports the earlier ACMG position, and
several professional organizations have subsequently altered
their positions.38–40 Data from two large studies show that for
“low risk women, the PPV for Down syndrome aer NIPS was
50–81% (N=55,244)24,25, and for “high risk women” this was
94% (N=72,382).25 NIPS and conventional screening were com-
pared and showed NIPS was superior with regards to PPV (80.9
vs. 3.4%, N=15,841).24 e NPV approached 100% for Down
Volume 18 | Number 10 | October 2016 | GENETICS in MEDICINE
Noninvasive prenatal screening for fetal aneuploidy: 2016 update | GREGG et al ACMG StAteMent
syndrome in these studies. Similarly, for Patau and Edwards
syndromes, the PPVs aer NIPS (Patau 33–90%, Edwards
50–70%)24,25 were superior to those with conventional screen-
ing (Patau 14%, Edwards 3.4%)24 and the NPV was 100% for
both conditions.23,24
High PPV provides benets to patients by enabling them to
more easily weigh the advantages and disadvantages of follow-
up diagnostic testing. Additional benets of NIPS include
earlier implementation with no gap across the gestational age
spectrum, unlike conventional screening methods. is allows
conrmatory diagnostic testing earlier in gestation and provides
a screening option for patients who present for care any time
aer the rst trimester. Earlier diagnosis facilitates providing
up-to-date, balanced, and accurate information at a time that
may enable patients to consider the broadest range of repro-
ductive options. In some cases, patients will elect to alter the
course of the pregnancy or pregnancy care; others will investi-
gate adoption or choose to learn about the expected outcome,
neonatal care, and long-term care for a child with disabilities.
• ACMG recommends:
○ Informing all pregnant women that NIPS is the most
sensitive screening option for traditionally screened
aneuploidies (i.e., Patau, Edwards, and Down
○ Referring patients to a trained genetics professional
when an increased risk of aneuploidy is reported aer
○ Oering diagnostic testing when a positive screening
test result is reported aer NIPS.
○ Providing accurate, balanced, up-to-date informa-
tion, at an appropriate literacy level when a fetus is
diagnosed with a chromosomal or genomic variation
in an eort to educate prospective parents about the
condition of concern. ese materials should reect
the medical and psychosocial implications of the
diagnosis41 (see Patient Resources).
○ Laboratories should provide readily visible and clearly
stated DR, SPEC, PPV, and NPV for conditions being
screened, in pretest marketing materials, and when
reporting laboratory results to assist patients and pro-
viders in making decisions and interpreting results.
○ Laboratories should not oer screening for Patau,
Edwards, and Down syndromes if they cannot report
DR, SPEC, and PPV for these conditions.
e expansion of NIPS to autosomes beyond 13, 18, and 21
is technically possible. Whole-chromosome fetal aneuploidy
other than these common aneuploidies most oen results
in early fetal loss.42 Counseling related to these rare auto-
somal aneuploidies is made dicult by limited case reports
and variable expressivity. Conned placental mosaicism
for chromosome 16 has been well described and results in
a spectrum of fetal outcomes from no clinical phenotype
to fetal growth restriction. In a large retrospective study
of amniocentesis performed for maternal age, ultrasound
ndings, biochemical abnormalities, or familial indications,
1/14,830 patients had trisomy 2, 8, 12, or 22.43 Detection
of lethal chromosome abnormalities for which the natural
course will be fetal loss has the potential to result in unnec-
essary diagnostic procedures and unnecessary pregnancy
termination procedures. In addition to having a personal
impact on patients, data collection in the public health
sector could result in inated pregnancy loss attributed to
diagnostic procedures and maternal complications from
pregnancy termination.
• ACMG does not recommend:
○ NIPS to screen for autosomal aneuploidies other than
those involving chromosomes 13, 18, and 21.
Fetal fraction
e placental fraction accounts for approximately 10% of all
cell-free DNA in maternal circulation.6,21,44 Data suggest that
the lower limit of cell-free fetal DNA for a reliable result is
approximately 4%. A no-call may be reported if there is not a
sucient amount of fetal cell-free DNA in the maternal blood
sample. In two prospective studies including more than 16,000
pregnancies, a low fetal fraction in maternal circulation was
associated with an increased risk of fetal aneuploidies.24,45 e
biologic mechanism of low fetal fraction and its association
with aneuploidies is speculative. Interestingly, triploidy was
most common (31%); however, trisomy 21 was seen in 23% of
cases of low fetal fraction.24 Others showed that a fetal fraction
of DNA in Down syndrome cases is oen the same or higher
when compared to pregnancies with euploid fetuses.46,47 Since
the introduction of NIPS into clinical practice, fetal fraction
has not been uniformly reported by laboratories. e described
relationship between low fetal fraction and increased risk of
aneuploidy adds to the importance of reporting the reason for a
no-call and of indicating in the report whether a low fetal frac-
tion was identied.
Factors that inuence fetal fraction include maternal
weight and gestational age.47–49 ere is no specic thresh-
old to describe the relationship between fetal fraction and
maternal weight. However, in cases of signicant obesity, a
no-call due to low fetal fraction should be anticipated. ere
is a gestational age threshold, below which results are not
reliable (9 or 10 weeks depending on the laboratory used).
Data suggest that before 20weeks, fetal fraction increases less
than 0.1% per week, which challenges the idea that repeating
sample collection is a viable approach to overcoming a low
fetal fraction.47,49
GENETICS in MEDICINE | Volume 18 | Number 10 | October 2016
GREGG et al | Noninvasive prenatal screening for fetal aneuploidy: 2016 update
ACMG StAteMent
• ACMG recommends:
○ Oering diagnostic testing for a no-call NIPS result
due to low fetal fraction if maternal blood for NIPS
was drawn at an appropriate gestational age. A repeat
blood draw is NOT appropriate.
○ Oering aneuploidy screening other than NIPS in
cases of signicant obesity.
○ All laboratories should include a clearly visible fetal
fraction on NIPS reports.
○ All laboratories should establish and monitor analyti-
cal and clinical validity for fetal fraction.
○ All laboratories should specify the reason for a no-call
when reporting NIPS results.
Long stretches of homozygosity
Single-nucleotide polymorphisms or array-based assays require
adequate heterozygosity between the maternal and fetal genomes
to provide meaningful data for the analysis of genomic balance
and copy number. erefore, stretches of homozygosity between
the maternal and fetal genomes render any dierences in copy
number within that region undetectable, including small duplica-
tions or deletions. In addition to preventing in the interpretation
of genomic balance, large regions of homozygosity for a single
chromosome may be suggestive of uniparental disomy (UPD),
whereas large regions of homozygosity dispersed over many
chromosomes may be suggestive of parental consanguinity.50
• ACMG recommends:
○ Informing patients that a no-call result may be due to
long stretches of homozygosity, which could be due to
either UPD or parental consanguinity.
○ Referring patients to a trained genetics professional
when a no-call result suspicious for UPD or parental
consanguinity is received.
○ Oering diagnostic testing with CMA when a no-call
result is obtained aer NIPS due to possible UPD or
parental consanguinity.
In one retrospective study of 88,970 amniocenteses, the diag-
nosis of any sex chromosome aneuploidy was made in 1/272
patients.43 is was higher for women older than 35 years
compared to younger women (1/210 and 1/459, respectively).
Conventional screening for aneuploidies does not detect
sex chromosome aneuploidies. e most common of these,
monosomy X (Turner syndrome), has been estimated to occur
in 1–1.5% of pregnancies51 and is a common cause of rst-
trimester pregnancy loss (~23%).52 e phenotype of individu-
als with a 47,XXX or 47,XYY karyotype is highly variable but
may include social or cognitive decits.53 Klinefelter syndrome
(47,XXY), however, does have a classic phenotype and is associ-
ated with sterility.53
e detection rate (clinical validity) of sex chromosome
aneuploidies aer NIPS is reported to be more than 90% and
has a false-positive rate of approximately 1%.54–57 e PPV
(clinical utility) for the aggregate of sex chromosome aneuploi-
dies among prospectively collected samples was 48.4% (range
for specic aneuploidies, 30–67%).57 A PPV in these ranges
is considerably higher than those accepted for conventional
screening of Patau, Edwards, and Down syndromes.
Etiologies of false-positive sex chromosome aneuploidy results
have been considered, and an approach to distinguish true positives
from false positives was described.58 Maternal medical, endocrine,
and fertility history can help to identify the cause of a false-positive
result. is includes patients with an organ transplantation from
either a 46,XY individual or unknown gender donor. Other causes
of false-positive results are similar to those for traditional aneu-
ploidies. ese include conned placental mosaicism, “vanishing”
twin or higher-order co-fetus, and, rarely, maternal neoplasm.
For these reasons, patients should be counseled about the advan-
tages and disadvantages of sex chromosome aneuploidy screening
within the construct of their preferences for information.
• ACMG recommends:
○ Informing all pregnant women, as part of pretest coun-
seling for NIPS, of the availability of the expanded use
of screening for sex chromosome aneuploidies.
○ Providers should make eorts to deter patients from
selecting sex chromosome aneuploidy screening for
the sole purpose of biologic sex identication in the
absence of a clinical indication for this information.
○ Informing patients about the causes and increased
possibilities of false-positive results for sex chromo-
some aneuploidies as part of pretest counseling and
screening for these conditions. Patients should also be
informed of the potential for results of conditions that,
once conrmed, may have a variable prognosis (e.g.,
Turner syndrome) before consenting to screening for
sex chromosome aneuploidies.
○ Referring patients to a trained genetics professional
when an increased risk of sex chromosome aneu-
ploidy is reported aer NIPS.
○ Oering diagnostic testing when a positive screening
test result is reported aer screening for sex chromo-
some aneuploidies.
○ Providing accurate, balanced, up-to-date informa-
tion and materials at an appropriate literacy level
when a fetus is diagnosed with a sex chromosome
aneuploidy in an eort to educate prospective parents
about the specic condition. ese materials should
reect medical and psychosocial implications for the
diagnosis41 (see Patient Resources).
○ Laboratories include easily recognizable and highly vis-
ible DR, SPEC, PPV, and NPV for each sex chromosome
aneuploidy when reporting results to assist patients and
providers in making decisions and interpreting results.
○ Laboratories should not oer screening for sex chro-
mosome aneuploidies if they cannot report DR, SPEC,
PPV, and NPV for these conditions.
Volume 18 | Number 10 | October 2016 | GENETICS in MEDICINE
Noninvasive prenatal screening for fetal aneuploidy: 2016 update | GREGG et al ACMG StAteMent
Conventional aneuploidy screening focuses on whole-
chromosome aneuploidies that have an overall live birth
frequency of 1/800 (Down syndrome)59 to 1/30,000 (Patau
syndrome). Expanding NIPS to include detection of specic
conditions caused by a CNV (e.g., 22q11.2 deletion, 1p36
deletion, 15q11.2–13 deletion) is technically possible (analytical
validity).60–63 e phenotypes associated with these conditions
can be severe; therefore, they may be appropriate conditions for
prenatal screening. However, providers and patients must be
aware that expanding the use of NIPS to include the detection
of CNVs requires in-depth knowledge of the limitations of the
technology, return of results, and follow-up.
Validation studies indicate a high detection rate (>97%) and
low false-positive rate (<1%) can be achieved. However, there
are few clinical utility studies. erefore, PPV and NPV have
been modeled.63–65 One report showed that for a specic combi-
nation of CNVs studied, PPV ranged from 3.8 to 17%. In a large
retrospective study of more than 21,000 samples, the aggregate
PPV for several CNVs screened simultaneously was 18% (spe-
cic conditions: 11–48%). Methods to improve PPV have been
reported.65 Modeling PPV and NPV is made more complex for
genome-wide analysis for which validation studies are limited
in scope and number.26,63 Determination of PPV and NPV is
hampered by the inherent limitations of studying multiple rare
conditions with variable expressivity. As greater portions of
the genome are analyzed for CNVs, false positive and negative
results are expected to increase. is may result in an increase
in patient anxiety and fetal procedures and a burden on an
already limited genetic counseling workforce.
Validation studies make the point that DR and SPEC depend on
many variables (e.g., depth of read),10,60–63 which can change the
false-positive and false-negative rate when NIPS is used for pre-
natal detection of CNVs. Pretest and posttest counseling is further
confounded by variable expressivity and penetrance of the condi-
tions being screened, size of the deletion being screened, specic
genes within the critical region of the locus interrogated, and the
number of genes within the critical region being screened.
• ACMG recommends:
○ Informing all pregnant women of the availability of the
expanded use of NIPS to screen for clinically relevant
CNVs when the following conditions can also be met:
• Obstetric care providers should discuss with
their patients the desire for prenatal screening
as opposed to diagnostic testing (i.e., CVS or
• Obstetric care providers should discuss with their
patients the desire for maximum fetal genomic
information through prenatal screening.
• Obstetric care providers should inform their
pati ents of the higher likelihood of false-positive
and false-negative results for these conditions as
compared to results obtained when NIPS is lim-
ited to common aneuploidy screening.
• Obstetric care providers should inform their pati-
ents of the potential for results of conditions that,
once conrmed, may have an uncertain prognosis.
○ Referring patients to a trained genetics professional
when NIPS identies a CNV.
○ Oering diagnostic testing (CVS or amniocentesis)
with CMA when NIPS identies a CNV.
○ Providing accurate, balanced, up-to-date information
at an appropriate literacy level when a fetus is diag-
nosed with a CNV in an eort to educate prospective
parents about the condition of concern. ese materi-
als should reect the medical and psychosocial impli-
cations of the diagnosis65 (see Patient Resources).
○ Laboratory requisitions and pretest counseling infor-
mation should specify the DR, SPEC, PPV, and NPV of
each CNV screened. is material should state whether
PPV and NPV are modeled or derived from clini-
cal utility studies (natural population or sample with
known prevalence).
○ Laboratories include easily recognizable and highly vis-
ible DR, SPEC, PPV, and NPV for each CNV screened
when reporting laboratory results to assist patients and
providers in making decisions and interpreting results.
Reports should state whether PPV and NPV are mod-
eled or derived from clinical utility studies (natural
population or sample with known prevalence). When
laboratories cannot report specic DR, SPEC, PPV,
and NPV, screening for those CNVs should not be per-
formed by that laboratory.
• ACMG does not recommend:
○ NIPS to screen for genome-wide CNVs. If this level
of information is desired, then diagnostic testing (e.g.,
chorionic villous sampling or amniocentesis) fol-
lowed by CMA is recommended.
Multiple gestation and/or donor oocytes:
ere are unique challenges when NIPS is used in multiple ges-
tation pregnancies conceived through donor oocytes. ese are
specic to the analytical method and bioinformatics employed
by the laboratory.
• ACMG recommends:
○ In pregnancies with multiple gestations and/or donor
oocytes, testing laboratories should be contacted
regarding the validity of NIPS before it is oered to
the patient as a screening option.
Unanticipated findings
Both constitutional and acquired forms of genomic imbal-
ance in the mother (e.g., aneuploidy of chromosome X,
microdeletions, neoplasia, chimerism due to allogenic organ
GENETICS in MEDICINE | Volume 18 | Number 10 | October 2016
GREGG et al | Noninvasive prenatal screening for fetal aneuploidy: 2016 update
ACMG StAteMent
or tissue transplantation, or mosaicism) and imbalances
within the fetoplacental genome (e.g., conned placental
mosaicism) can give rise to identiable bioinformatic pat-
terns that may confound interpretations. erefore, provid-
ers should be aware of the potential for false-positive results
that may resolve aer diagnostic testing. Although it is not
the purpose of NIPS to identify clinically relevant maternal
genomic information, patients and providers should be aware
of the potential for inadvertent discovery of such information
and the potential for additional follow-up testing unrelated
to the pregnancy.
Given the dierences in laboratory methodologies and bioin-
formatic processing that may be used, it is beyond the scope of
this document to address considerations that might be unique
to any specic method in use. It therefore remains the respon-
sibility of each laboratory to make physician providers aware of
clinically relevant features that are specic to the methodology
used. is is best accomplished through educational materials
and laboratory reports.
• ACMG recommends:
○ Informing patients of the possibility of identifying
maternal genomic imbalances and that this possibility
depends on the specic methodology used.
○ Referring patients to a trained genetics professional
when NIPS identies maternal genomic imbalances.
○ Oering aneuploidy screening other than NIPS for
patients with a history of bone marrow or organ
transplantation from a male donor or donor of uncer-
tain biologic sex.
○ Discussing the possibility of discordant fetal biologic
sex if maternal blood transfusion was performed <4
weeks prior to the blood draw for NIPS.
Positive and negative predictive values
Understanding the importance of PPV is paramount to screen-
ing. PPV is a screening test metric that is useful when patients
screen positive. is metric is used by patients in deciding the
next steps in decision making. Because the specicity is so high
aer NIPS for traditionally screened aneuploidies, NPV is less
oen the focus. However, it is one of the key features of this
technology. A high NPV oers patients reassurance in the post-
test setting. ere are several mathematical approaches that can
be used to model PPV and NPV from validation data. PPV for
aneuploidy is very sensitive to prevalence/a priori risk, and to a
lesser extent DR and SPEC, which do not uctuate with mater-
nal age. Maternal age is a highly important factor in determin-
ing the prevalence of Down syndrome and other aneuploidies,
but it is not a factor when considering CNVs. One reason why
PPV is much lower for detection of CNVs is that the prevalence
and detection rate are low compared to traditionally screened
aneuploidies. A common error is to interpret PPV across an
entire population without taking into account patient-specic
information (e.g., prevalence based on maternal age when
ere are several online calculators for determining
patient-specic PPV and NPV aer NIPS (e.g., http://secure. PPV seems
irrelevant to anyone not facing a positive test result. If the
PPV of each condition being considered were reported when
results were negative, then there would be an excess of data
cluttering a report.
• ACMG recommends:
○ Laboratories provide patient-specic PPV when
reporting positive test results.
○ Laboratories provide population-derived PPV when
reporting positive results in cases in which patient-
specic PPV cannot be determined due to unavailable
clinical information.
○ Laboratories provide modeled PPV when reporting
positive results for which neither patient-specic nor
population-derived PPV are possible.
○ Providers use validated online calculators to provide
patient-specic PPV when results from NIPS are pos-
itive to facilitate clear and accurate communication
with patients.
○ Incorporating laboratory-specic DR and SPEC to
provide clear and patient-specic information when
using validated online calculators.
In a consensus statement by the ACMG, the American College
of Obstetricians and Gynecologists (ACOG), the National
Society of Genetics Counselors (NSGC), and Down syndrome
organizations, there was unanimous agreement that patient
education materials about prenatal testing and associated con-
ditions should result from “collaboration among healthcare and
advocacy organizations.41 According to Public Law 110–371
enacted in 2008, “partnerships between healthcare professional
groups and disability advocacy organizations” were empha-
sized regarding the collection, synthesis, and dissemination
of “current evidence-based information” related to prenatal
conditions. With these charges in mind, the ACMG has identi-
ed available patient resources (listed alphabetically) that have
resulted from collaborations between healthcare professional
groups and advocacy organizations.
Down Syndrome Pregnancy (http://downsyndromepreg- is site, for expectant parents preparing
for the birth of a baby with Down syndrome, provides a range
of books in English and Spanish that are recommended in the
“NSGC Guidelines for Communicating a Prenatal or Postnatal
Diagnosis of Down Syndrome” and that have been reviewed by
medical and patient advocacy experts.
Genetics Home Reference ( is
online reference provides information for patients and families
about more than 1,000 genetic conditions. All content is written
by a full-time sta with backgrounds in genetics, reviewed by
outside experts, and contains input from support and advocacy
Volume 18 | Number 10 | October 2016 | GENETICS in MEDICINE
Noninvasive prenatal screening for fetal aneuploidy: 2016 update | GREGG et al ACMG StAteMent
organizations. Genetics Home Reference is a service of the
National Library of Medicine, which is part of the National
Institutes of Health, an agency of the US Department of Health
and Human Services.
Genetic Support Foundation (https://www.geneticsup- is nonprot organization, founded by
genetics professionals, provides information about pregnancy
and genetics and the dierent conditions that can be detected
prenatally. It oen includes instructional videos.
Lettercase/e National Center for Prenatal and Postnatal
Resources ( Lettercase oers profes-
sionally reviewed materials about genetic conditions. Currently,
“Understanding a Down Syndrome Diagnosis” and “Understanding
a Turner Syndrome Diagnosis” are available in print and digital ver-
sions in several languages. e materials are intended for expect-
ant couples who have received a prenatal diagnosis of Down or
Turner syndrome but have not yet made a decision regarding their
pregnancy options. e materials are prepared with assistance
from the ACMG, ACOG, NSGC, and national patient advocacy
NSGC “Fact Sheet about Down Syndrome for New and
Expectant Parents” (d=387) and
A Patient’s Guide to Understanding Noninvasive Prenatal
Testing” (d=385). ese fact sheets
on the NSGC website, which provide basic downloadable
information, were reviewed by the National Society of Genetic
Counselors Down Syndrome Information Act Working Group,
with assistance from the National Center for Prenatal and
Postnatal Resources.
e following resources (listed alphabetically) were created by
respected medical organizations or medical expert consensus
and can serve as useful references for medical providers.
Delivering a diagnosis. Resources describing simulation
training for healthcare professionals who deliver a prenatal
diagnosis to expectant couples are available. ese projects
were funded by federal grants and ecacy was researched and
Down syndrome healthcare guidelines. “Healthcare
Supervision for Children with Down Syndrome” (http:// is was
written by the Committee on Genetics of the American
Academy of Pediatrics, provides guidance for healthcare pro-
fessionals. Resources for parents are also listed.
GeneReviews (
NBK1116). is online resource for clinicians provides peer-
reviewed information written by medical experts. Information is
updated every 2 to 4 years through a formal review process. It
is an excellent source of information, and physicians faced with
a need to learn about common CNVs may nd this resource
“Care of Girls and Women with Turner Syndrome: A
Guideline of the Turner Syndrome Study Group. is was
written by the Turner Syndrome Consensus Study Group of the
National Institutes of Health and was adopted by the American
Academy of Pediatrics.68
22q11 deletion syndrome (DiGeorge syndrome) guide-
lines. Peer-reviewed expert consensus documents are available
for the evaluation and management of patients with 22q11 dele-
tion syndrome (DiGeorge syndrome).69,70 is is the most com-
mon copy-number variation currently being oered through
NIPS. Resources for other CNVs may be found in GeneReviews.
New data and provider and patient demands require an updated
position on the use of NIPS in prenatal care. We provide a frame-
work for understanding how genetic technology moves from
an idea into clinical practice. We hope this framework helps to
explain ACMGs recommendations. Clinical validation strongly
suggested that NIPS can replace conventional screening for Patau,
Edwards, and Down syndromes. Objective measures of clinical
utility support this. Test metrics support NIPS across the maternal
age spectrum and continuum of gestational age beginning at 9–10
weeks as long as patients are not signicantly obese. In the latter
case, fetal fraction leading to an inability to make a call is limiting.
We have raised the bar for pretest counseling by expanding
NIPS beyond that for Patau, Edwards, and Down syndromes.
Providers should have a thorough understanding of patient pref-
erences; eorts to educate about the limitations are not trivial.
Although clinical utility studies are limited, they point to a role
for NIPS in sex chromosome aneuploidy screening and screening
for selected CNVs. We support these uses when the live birth fre-
quency of conditions reaches or exceeds that of currently screened
conditions and when test metrics meet or exceed those of well-
established approaches to prenatal screening. Furthermore, we
considered the potential for children to be impacted by early treat-
ment. Our recommendations will aect communication between
providers and patients and between providers and testing labora-
tories. Laboratories are encouraged to meet the needs of providers
and patients by delivering meaningful screening reports, engag-
ing in education, and identifying ways to address distributive jus-
tice, a medical ethical principle that challenges genomics-based
innovative and clinically useful technologies.
The ACMG Noninvasive Prenatal Screening Work Group is grate-
ful to Marsha Harben of the University of Florida for her tireless
assistance in the preparation of this document.
B.G.S. serves on the Advisory Board of several nonprofit entities
providing education about Down syndrome. The other authors
declare no conflict of interest.
GENETICS in MEDICINE | Volume 18 | Number 10 | October 2016
GREGG et al | Noninvasive prenatal screening for fetal aneuploidy: 2016 update
ACMG StAteMent
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GENETICS in MEDICINE | Volume 18 | Number 10 | October 2016
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Background: Current cell-free DNA assessment of fetal chromosomes does not analyze and report on all chromosomes. Hence, a significant proportion of fetal chromosomal abnormalities are not detectable by current noninvasive methods. Here we report the clinical validation of a novel noninvasive prenatal test (NIPT) designed to detect genomewide gains and losses of chromosomal material ≥7 Mb and losses associated with specific deletions <7 Mb. Objective: The objective of this study is to provide a clinical validation of the sensitivity and specificity of a novel NIPT for detection of genomewide abnormalities. Study design: This retrospective, blinded study included maternal plasma collected from 1222 study subjects with pregnancies at increased risk for fetal chromosomal abnormalities that were assessed for trisomy 21 (T21), trisomy 18 (T18), trisomy 13 (T13), sex chromosome aneuploidies (SCAs), fetal sex, genomewide copy number variants (CNVs) ≥7 Mb, and select deletions <7 Mb. Performance was assessed by comparing test results with findings from G-band karyotyping, microarray data, or high coverage sequencing. Results: Clinical sensitivity within this study was determined to be 100% for T21 (95% confidence interval [CI], 94.6-100%), T18 (95% CI, 84.4-100%), T13 (95% CI, 74.7-100%), and SCAs (95% CI, 84-100%), and 97.7% for genomewide CNVs (95% CI, 86.2-99.9%). Clinical specificity within this study was determined to be 100% for T21 (95% CI, 99.6-100%), T18 (95% CI, 99.6-100%), and T13 (95% CI, 99.6-100%), and 99.9% for SCAs and CNVs (95% CI, 99.4-100% for both). Fetal sex classification had an accuracy of 99.6% (95% CI, 98.9-99.8%). Conclusion: This study has demonstrated that genomewide NIPT for fetal chromosomal abnormalities can provide high resolution, sensitive, and specific detection of a wide range of subchromosomal and whole chromosomal abnormalities that were previously only detectable by invasive karyotype analysis. In some instances, this NIPT also provided additional clarification about the origin of genetic material that had not been identified by invasive karyotype analysis.
Full-text available
Objective To evaluate the clinical performance of non-invasive prenatal testing for trisomy 21, 18, and 13 using targeted cell-free DNA analysis.Methods Targeted cfDNA analysis using DANSR™ and FORTE™ with microarray quantitation was used to evaluate the risk of trisomy 21, 18, and 13 in blinded samples from 799 singleton, twin, natural and IVF pregnancies. Subjects either had fetal chromosome evaluation by karyotype, FISH, QF-PCR, or karyotype for newborns with suspected aneuploidy at birth. The results of targeted cfDNA analysis were compared to clinical genetic testing outcomes to assess clinical performance.ResultsTargeted cfDNA analysis with microarray quantification identified 107/108 trisomy 21 cases (99.1%), 29/30 trisomy 18 cases (96. 7%), and 12/12 trisomy 13 cases (100%). The specificity was 100% for all three trisomies. Combining this data with all published clinical performance studies using DANSR/FORTE methodology for greater than 23,000 pregnancies, the sensitivity of targeted cfDNA analysis was calculated to be greater than 99% for trisomy 21, 97% for trisomy 18, and 94% for trisomy 13. Specificity for each trisomy was greater than 99.9%.Conclusion Targeted cfDNA analysis demonstrates consistently high sensitivity and extremely low false positive rates for common autosomal trisomies in pregnancy across quantitation platforms. This article is protected by copyright. All rights reserved.
The American College of Medical Genetics and Genomics (ACMG) believes that advances in genetic technology should be considered carefully before they become part of routine clinical care. The organization has defined a standard of care for prenatal/preconception population carrier screening for common single-gene autosomal recessive disorders. With advances in genetic sequencing and microarray hybridization analysis, large quantities of disease-specific genetic variants can be determined in a time frame suited to prenatal/preconception screening and diagnosis. Commercial laboratories offer expanded carrier screening panels, but no professional guidance has been forthcoming on which disease genes and mutations to include. The proper selection of appropriate disease-causing targets for general population-based carrier screening should be developed using clear criteria rather than including as many disorders as possible. Disorders should be of a nature that most at-risk patients and their partners identified would consider having a prenatal diagnosis to facilitate making decisions about reproduction. The inclusion of disorders characterized by variable expressivity or incomplete penetrance and those associated with a mild phenotype should be optional and made transparent when these technologies are used for screening (ethical principle of nonmaleficence). When adult-onset disorders are included, patients must provide consent to screening for these conditions, especially if they have implications for the health of the individual being screened or other family members (ethical principles of autonomy and nonmaleficence). For each disorder, the causative genes, mutations, and mutation frequencies should be known in the population being tested to allow meaningful assessment of residual risk in individuals who test negative. Laboratories should specify how residual risk is calculated using pan-ethnic population data or a specific race/ethnic group. This calculation requires knowledge of the carrier frequency within a population and the proportion of disease-causing alleles detected using the specific testing platform. Laboratories offering expanded carrier screening should keep data and regularly report findings that allow calculation of residual risk estimates for all disorders being offered. There must be validated clinical association between the mutation(s) detected and the severity of the disorder. Materials must include specific citations that support inclusion of the mutations for which screening is being performed. Quality control and proficiency testing must comply with the ACMG Standards and Guidelines for Clinical Genetics Laboratories and should include the entire process of preanalytic, analytic, and postanalytic phases. A multifactorial approach will require a more generic consent process than is generally used for single-disease screening because it may not be practical for clinicians to discuss each disease included in a multidisease carrier screening panel. A pamphlet or Web site containing a brief description of each disorder included in a test panel should be available to patients. Genetic counseling before and after testing should be available, especially for those who have positive results. This counseling should include disclosure of the mutation(s) detected, description of the clinical nature of the disorder, facilitation of testing of the reproductive partner, calculation of the revised fetal risk when the partner is not available or declines testing, identification of other at-risk family members, and discussion of options for fetal testing and reproductive decision making.
Purpose: No studies to date have reported an estimated number of live births, elective terminations, and natural losses (miscarriages and stillbirths) for Down syndrome (DS) in Massachusetts (MA). These numbers would be helpful to estimate how many expectant parents of children with DS need support and the number of live-born children with DS who require services. Methods: Combining robust data sets, including the Annual Reports of the MA Birth Defects Monitoring Program, we estimated the number of live births, elective terminations, and natural losses with Down syndrome from 1900 to 2010. Results: The live birth prevalence for DS in MA for the most recent years for which data are available (2006-2010) was estimated at 12.4 per 10,000 live births, with a total of approximately 94 live births annually. During this period, an estimated 126 DS-related elective pregnancy terminations were performed in MA annually. As of 2008, the estimated rate at which live births with DS was reduced as a consequence of DS-related elective pregnancy terminations was 49%. Conclusion: The reduction of live births with DS is significantly higher in MA than in the rest of the United States as a whole. However, ethnic and racial differences in reduction rates were similar-highest for Asians/Pacific Islanders, followed by non-Hispanic whites, non-Hispanic blacks/Africans, and Hispanics.Genet Med 18 5, 459-466.
Objective: To use a decision-analytic model to assess a comprehensive set of outcomes of prenatal genetic testing strategies among women of varying ages. Methods: We assessed outcomes of six testing strategies incorporating diagnostic testing with chromosomal microarray, multiple marker screening, cell-free DNA screening, and nuchal translucency screening alone, in combination, or in sequence. Clinical outcomes included prenatal detection or birth of a neonate with a significant chromosomal abnormality and diagnostic procedures performed. Other outcomes included maternal quality-adjusted life-years and costs. Sensitivity analyses were conducted to examine the robustness of the findings. Results: At all ages assessed, screening strategies starting with multiple marker screening offered the highest detection rate when all chromosomal abnormalities were considered. Incorporating cell-free DNA as an optional secondary screen decreased the number of diagnostic procedures, but also decreased the number of abnormalities diagnosed prenatally, resulting in a similar number of procedures per case diagnosed at age 30 years; the option of secondary cell-free DNA screening becomes more favorable at older ages. Multiple marker screening with optional follow-up diagnostic testing was the most effective (highest quality-adjusted life-years) and least expensive strategy at ages 20-38 years. At age 40 years or older, cell-free DNA screening was optimal with an incremental cost-effectiveness ratio of $73,154 per quality-adjusted life-year. Conclusion: When considering all detectable chromosome problems as well as patient preferences and baseline risks, multiple marker screening with the option of diagnostic testing for screen-positive results is the optimal strategy for most women. At age 40 years and older, cell-free DNA as a primary screen becomes optimal and is cost-effective. Level of evidence: II.
The development of non-invasive prenatal testing has increased accessibility of fetal testing. Companies are now advertising prenatal testing for aneuploidy via the Internet. The aim of this systematic review of websites advertising non-invasive prenatal testing for aneuploidy was to explore the nature of the information being provided to potential users. We systematically searched two Internet search engines for relevant websites using the following terms: 'prenatal test'; 'antenatal test'; 'non-invasive test'; 'noninvasive test'; 'cell-free fetal DNA'; 'cffDNA'; 'Down syndrome test' or 'trisomy test'. We examined the first 200 websites identified through each search. Relevant web-based text was examined and key topics were identified, tabulated and counted. To analyse the text further, we used thematic analysis. Forty websites were identified. While a number of sites provided balanced, accurate information, in the majority supporting evidence was not provided to underpin the information and there was inadequate information on the need for an invasive test to definitely diagnose aneuploidy. The information provided on many websites does not comply with professional recommendations. Guidelines are needed to ensure that companies offering prenatal testing via the Internet provide accurate and comprehensible information. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
Objective Sufficient fetal DNA in a maternal plasma sample is required for accurate aneuploidy detection via noninvasive prenatal testing, thus highlighting a need to understand the factors affecting fetal fraction.Method The MaterniT21TM PLUS test uses massively parallel sequencing to analyze cell-free fetal DNA in maternal plasma and detect chromosomal abnormalities. We assess the impact of a variety of factors, both maternal and fetal, on the fetal fraction across a large number of samples processed by Sequenom Laboratories.ResultsThe rate of increase in fetal fraction with increasing gestational age varies across the duration of the testing period, and is also influenced by fetal aneuploidy status. Maternal weight trends inversely with fetal fraction, and we find no added benefit from analyzing BMI or blood volume instead of weight. Strong correlations exist between fetal fractions from aliquots taken from the same patient at the same blood draw, and also at different blood draws.Conclusion While a number of factors trend with fetal fraction across the cohort as a whole, they are not the sole determinants of fetal fraction. In this study, the variability for any one patient does not appear large enough to justify postponing testing to a later gestational age.
Resequencing NIPT samples that receive a high-risk call for the 22q11.2 deletion at a higher depth-of-read increases the PPV without decreasing sensitivity. Copyright © 2015 Elsevier Inc. All rights reserved.