Prenatal diagnosis enables early diagnosis of congeni-
tal anomalies and genetic disorders in utero. The pop-
ulation risk of having a child with some congenital
abnormality, whether genetically and/or environmen-
tally determined, varies between 3 and 5%. In families
at risk of a genetic disorder the probability of having
an affected child can exceed several fold the popula-
tion risk, therefore in these families prenatal diagnos-
tic procedures should be strictly applied .
Advanced imagining techniques as well as cytoge-
netic and molecular biology methods provide the
means to diagnose prenatally numerous congenital
structural malformations and genetic disorders in high-
risk families. Early diagnosis in utero can prove essen-
tial to management of the pregnancy, prenatal and
postnatal medical care, and treatment. It is also crucial
to making informed decisions about continuing or ter-
minating the pregnancy.
Genetic counseling in association with modern pre-
natal diagnostic procedures constitutes a basic element
of prevention of congenital anomalies and genetic dis-
orders. The process of prenatal counseling and diagno-
sis is committed mainly to transferring information
which aims to help the parents to:
1. understand and acknowledge the indications for
2. understand the medical aspects of making the diag-
nosis of a genetic disease or a congenital abnor-
mality (by characterizing the disorder, pattern of
inheritance, the risk of having an affected child in
3. make informed choices about the adequate for a
given pathology and acceptable diagnostic scheme
(by describing the potential diagnostic methods and
procedures, their benefits, limitations and risks).
Vol. 45, Supp. 1, 2007
Prenatal diagnosis - principles of diagnostic procedures
and genetic counseling
Stembalska Agnieszka, Ryszard Œlêzak, Karolina Pesz, Justyna Gil,
Maria M. S¹siadek
Department of Genetics, Wroc³aw Medical University, Wroc³aw, Poland
Abstract: The frequency of inherited malformations as well as genetic disorders in newborns account for around 3-5%.
These frequency is much higher in early stages of pregnancy, because serious malformations and genetic disorders usually
lead to spontaneous abortion. Prenatal diagnosis allowed identification of malformations and/or some genetic syndromes in
fetuses during the first trimester of pregnancy. Thereafter, taking into account the severity of the disorders the decision
should be taken in regard of subsequent course of the pregnancy taking into account a possibilities of treatment, parent's
acceptation of a handicapped child but also, in some cases the possibility of termination of the pregnancy. In prenatal test-
ing, both screening and diagnostic procedures are included. Screening procedures such as first and second trimester bio-
chemical and/or ultrasound screening, first trimester combined ultrasound/biochemical screening and integrated screening
should be widely offered to pregnant women. However, interpretation of screening results requires awareness of both sen-
sitivity and predictive value of these procedures. In prenatal diagnosis ultrasound/MRI searching as well as genetic proce-
dures are offered to pregnant women. A variety of approaches for genetic prenatal analyses are now available, including
preimplantation diagnosis, chorion villi sampling, amniocentesis, fetal blood sampling as well as promising experimental
procedures (e.g. fetal cell and DNA isolation from maternal blood). An incredible progress in genetic methods opened new
possibilities for valuable genetic diagnosis. Although karyotyping is widely accepted as golden standard, the discussion is
ongoing throughout Europe concerning shifting to new genetic techniques which allow obtaining rapid results in prenatal
diagnosis of aneuploidy (e.g. RAPID-FISH, MLPA, quantitative PCR).
Key words: Prenatal diagnosis - Prenatal screening - Prenatal rapid testing - Prenatal genetic counseling
Correspondence: M. M. S¹siadek, Dept. of Genetics, Wroc³aw
Medical University, Marcinkowskiego Str. 1, 50-367 Wroc³aw,
Poland; tel. (+4871) 7841256, fax.: (+4871) 7840063,
The decision about prenatal diagnosis should be
made solely by the woman/couple concerned (the prin-
ciple of informed consent). The genetic counselor
serves only as an advisory body (non-directional coun-
seling) for the patient and enables her to consider and
assess the advantages and disadvantages of suggested
However, it is receiving the genetic and clinical
diagnosis (the interpretation of the test result) and the
consequences of diagnosing a syndrome or fetal anom-
alies (informed decision about continuing or terminat-
ing the pregnancy) that are crucial points in the coun-
According to WHO and European Commission's
recommendations, prenatal diagnosis should be volun-
tary and performed only in order to gain knowledge
about fetal health status (as described by medical indi-
cations). Feasibility of prenatal diagnosis should be
equal, fair, and available to anyone, irrespective of the
couple's or medical practitioner's attitude towards ter-
mination of pregnancy. In case of receiving an abnor-
mal result the decision about termination of the preg-
nancy should be made independently by the woman or
the couple. People making such decisions should not
be discriminated against, whatever decision they have
made: either terminating the pregnancy or giving birth
to a handicapped child [1,2].
Prenatal diagnosis techniques
Methods of prenatal diagnosis can be divided into
non-invasive and invasive techniques.
Used for diagnosing congenital anomalies and risk
assessment of given genetic disorders (screening) 
– routine obstetric ultrasound scan
– high-resolution ultrasound scan and Doppler
– fetal heart echocardiography
• magnetic resonance imaging (MRI)
• maternal serum biochemistry testing (measure-
ment of indicative enzymes in maternal blood
Routine obstetric ultrasound scanning. Performed
by the obstetrician managing the pregnancy. Standards
for normal pregnancies provide for four scans carried
out at: 11-14 weeks, 21-26 weeks, 27-32 weeks, and
40 week of gestation (as recommended by the Ministry
of Health, 10 July 2003).
High resolution ultrasound scanning. Performed in
any pregnancy with an increased risk of fetal structur-
al abnormalities, isolated or part of a genetic syndrome
(Table 1). Women are referred for high-resolution
ultrasound to specialist centers managing high-risk
pregnancies. According to the Ultrasound Section of
Polish Gynecological Society's recommendations the
first scan should take place at 11-13 (+6 days) weeks
of gestation (crown rump length 45-84 mm), followed
by another scan at 18-23 weeks of gestation.
In recent years three-dimensional ultrasound (3D)
and four-dimensional ultrasound (4D) have started to
play an increasing role in prenatal diagnosis. They can
be applied in assessing facial features, central nervous
system abnormalities and skeletal defects .
Doppler studies. Detect abnormal blood flow in
umbilical, placental, and fetal vessels that may be sug-
gestive of a genetic syndrome (Table 1).
Fetal heart echocardiography. Performed at 18-23
weeks of gestation in the presence of an increased risk
of heart defect (for example: heart defect in a parent or
sibling, abnormal routine ultrasound) .
Magnetic Resonance Imaging. MRI is used in com-
bination with ultrasound, usually at or after 18 weeks'
gestation. MRI provides a tool for examination of
fetuses with large or complex anomalies, and visuali-
zation of the abnormality in relation to the entire body
of the fetus. Apparently MRI is a risk-free method .
Biochemistry testing (maternal serum markers) can
be applied as a screening technique for every pregnant
Screening in the first trimester involves the meas-
urement of PAPP-A(pregnancy associated plasma pro-
tein A) and free -HCG ( -human chorionic
gonadotropin) levels in maternal serum. These meas-
urements are used in conjunction with ultrasound
scanning that includes assessment of ultrasound mark-
ers such as nuchal translucency (NT) thickness and
absence/presence of the nasal bone (NB). The detec-
tion rate (DR) of these combined methods is about 85-
90% in regard to trisomy 21 and 18, for a false positive
rate of 5%. DR for nuchal translucency alone is 75%
for a false positive rate of 5%. Abnormal nuchal
translucency thickness measurements can be associat-
ed with other disorders such as: heart defects, Beck-
with-Wiedemann syndrome, achondroplasia, Smith-
Lemli-Opitz syndrome, osteogenesis imperfecta, Noo-
nan syndrome, and with pregnancies complicated by
arterial hypertension or gestosis .
Recent studies have indicated the possibility of
introducing a new biochemical marker for Down and
Edwards syndrome: ADAM 12 (A Disintegrin And
Metalloprotease 12) that can be used in the first
trimester screening. Combining ADAM 12, PAPP-A,
A. Stembalska et al.
β-HCG and NT measurements at 8-9 and 12-13 weeks
of gestation increases the DR to 97%, for a false posi-
tive rate of 1% [8-10].
Second trimester maternal serum biochemistry (at
14-18 weeks of gestation) involves the "triple",
"quadruple" (triple screen and inhibin A) and "inte-
The "triple" screen is the measurement of alpha-
fetoprotein (AFP), free beta human chorionic
gonadotropin (β-HCG), free estriol (uE3) levels in
maternal serum. The values of these parameters can be
influenced by the presence of maternal diabetes type 1,
smoking and pregnancy-related weight gain . The
detection rate for this test is increased by determining
the Ulm index (which eliminates the influence of
maternal age on test results). Second trimester mater-
nal serum biochemical testing is carried out as a
screening method for Down and Edwards syndrome,
open neural tube defects (anencephaly, myomeningo-
cele, omphalocele and gastroschisis). DR for trisomy
21 and 18 is 60-70%, for a false positive rate of 6%.
Abnormal second trimester maternal serum biochemi-
cal test results are an indication for high-resolution
ultrasound in the second and third trimester and/or
invasive prenatal diagnosis. Evaluation of the severity
and the etiology of the anomaly is an important prog-
nostic factor .
Invasive procedures involve direct examination of
fetal cells or tissues. Classical cytogenetic, molecular
and biochemical methods (performed on uncultured or
cultured cells) are the most frequently used in prenatal
invasive diagnosis. The procedures should take place
in specialist centers that manage high-risk pregnan-
cies. When considering invasive methods all indica-
tions and criteria need to be carefully evaluated as
there is a considerable risk to the pregnancy .
Invasive techniques include:
•chorionic villus sampling (trophoblast cells
•amniocentesis (amniotic fluid cells analysis)
•cordocentesis (Percutaneous Umbilical Blood
Chorion villi sampling (CVS) - a sample of the devel-
oping placenta is obtained transcervically or transab-
dominally at 8-11 weeks of gestation under ultrasound
guidance. A variety of diagnostic techniques can be
employed on CVS cells:
• karyotype analysis (classical and molecular
cytogenetic methods) - detects all numerical and
many structural chromosome aberrations,
including microdeletions that cause syndromes
such as Prader-Willi or William's syndrome,
•enzyme studies, for example when there is a risk
of inborn errors of metabolism (phenylke-
tonuria, Gaucher disease, mucopolysaccharido-
sis, haemoglobinopathies such as thalassaemia),
•DNA analyses in monogenic disease (a pre-
ferred method for molecular studies).
Table 1. Ultrasound markers of fetal congenital abnormalities or
genetic syndromes found in: (A) first trimester scanning [at 11-13
(+6 days ) weeks' gestation], (B) second trimester scanning [at 18-
24 (+6 days ) weeks' gestation].
The risk to the pregnancy is about 2% (most fre-
quently: miscarriage, infection, bleeding, limb
defects). The benefit of CVS is an early diagnosis and
the chance to verify the results by other invasive
The following problems may arise in CVS:
•placental mosaicism (confined to trophoblast
tissue not fetal tissue),
• contamination by maternal tissue .
Amniocentesis - can be performed at 13-15 weeks of
gestation (early amniocentesis) but usually done at 16-
18 weeks of gestation. A sample of about 15 ml of
amniotic fluid is obtained transabdominally under
Employed methods of analysis include:
•karyotyping (cytogenetic as well as molecular
• DNA analysis (monogenic disease diagnosis,
such as congenital adrenal hyperplasia, cystic
• biochemical studies:
– measurement of AchE and AFP levels when
considering neural tube defects
– measurement of 17α-hydroprogesterone
when a risk of congenital adrenal hyperplasia
– inborn errors of metabolism diagnosis
(mucopolysaccharidosis, familial hypercho-
lesterolaemia, adrenoleucodystrophy, homo-
cysteinuria, maple syrup urine disease)
The risk of amniocentesis is around 0.5-1% and it
includes miscarriage, transient amniotic fluid leakage
and intrauterine infection .
Cordocentesis (Percutaneous Umbilical Blood
Sampling) - a sample of 0.5-1 ml fetal blood is
obtained from the umbilical vein (close to the placen-
ta) usually at 18-23 weeks of gestation under ultra-
sound guidance. The blood sample can be used for
genetic and biochemical studies, including chromoso-
mal analysis and monogenic disease diagnosis
(phenylketonuria, cystic fibrosis, Duchenne muscular
dystrophy). Furthermore it is also possible to detect
haemoglobinopathies, immunological deficiency syn-
dromes (ataxia-teleangiectasia) and intrauterine infec-
tions (toxoplasmosis, rubella, cytomegaly).
The risk is estimated to be around 2% with fetal
death, premature birth, bleeding (usually transient) and
fetal bradycardia (usually short lasting) being the most
frequent complications .
Optimal diagnostic algorithm
The criteria for prenatal diagnosis classification are
presented in Table 2 (low-risk and high-risk pregnan-
cies). The approach to prenatal diagnosis in these
groups is aimed at 1) estimating early and accurately
the risk of genetic disorder or congenital abnormality
in the fetus (genetic counseling), 2) choosing the
appropriate diagnostic methods (informed decision).
The optimal time for genetic counseling referral is
10th week of gestation . This is early enough to
implement the correct diagnostic scheme: risk evalua-
tion, effective non-invasive procedures, and invasive
diagnosis if warranted.
The best approach to prenatal diagnosis in a lower-
risk pregnancy (example: high level of anxiety)
involves referring the woman for genetic counseling
(family history, pedigree analysis), risk evaluation and
implementing non-invasive methods such as high-res-
olution ultrasound scan with nuchal translucency
thickness assessment and screening tests: PAPP-A at
11-13(+6) weeks' gestation and/or "triple" test at 14-16
weeks' gestation. Invasive procedures may be imple-
mented in case of abnormal screening results. An indi-
vidual approach to non-invasive methods can depend
on some other factors, for example the kind of con-
genital abnormality found in the previous child. In
case of neural tube defects the algorithm includes:
1. folic acid supplementation (4 mg) preconceptually
(at least 3 months) continuing throughout 12 weeks
2. AFP/AchE measurements in amniotic fluid
3. "triple" screen of maternal serum at 14-16 weeks of
4. high-resolution ultrasound or MRI.
The classical approach to prenatal diagnosis in
high-risk pregnancies (example: high-risk of fetal ane-
uploidy because of advanced maternal age) includes:
1. ultrasound scan with nuchal translucency thickness
evaluation and assessment of the presence/absence
of nasal bone at 11-13(+6) weeks' gestation
2. PAPP-A and β-HCG measurements in maternal
serum at 11-13(+6) weeks' gestation 
3. amniocentesis at 13-17 weeks' gestation - fetal
karyotype analysis [13,18]
4. high-resolution ultrasound scan at 20-24 weeks'
In most clinical situations an individual approach to
prenatal diagnosis is necessary depending on indica-
tions for prenatal diagnosis, time of gestation at genet-
ic counseling referral and maternal age. For example
biochemistry testing is not recommended to women
above 42 years of age, as there is a high risk of obtain-
ing false results.
A woman who receives a prenatal diagnosis result
that indicates serious fetus abnormality may consider
continuing or terminating the pregnancy according to
the current state of the law. If the pregnancy is to be
A. Stembalska et al.
continued it should be treated as high-risk and appro-
priate preparations should take place in order to imple-
ment treatment in utero if available and provide best
possible medical care just after birth.
Genetic prenatal diagnosis
The development of genetic and molecular biology
methods has opened up new opportunities in genetic
prenatal diagnosis. Standard methods are based on cul-
turing fetal cells and then implementing classical and
molecular cytogenetic techniques or molecular meth-
ods. It takes on average 1 to 3 weeks to obtain a defin-
itive result, the time depending on the method .
The increase in the number of invasive tests
requires the introduction of reliable and rapid testing
methods in regard to common chromosomal numerical
aberrations (chromosome 13, 18, 21, X and Y aneu-
ploidies) as well as rare genetic syndromes/disorders
Currently in Europe there is an on-going discussion
about allowing for changes to prenatal diagnosis algo-
rithms because of the introduction of new rapid diag-
nostic techniques (Rapid Tests - RT), of chosen chro-
mosomal defects. These recommended diagnostic
1. Rapid-FISH (rapid fluorescence in situ hybridiza-
2. MLPA (multiple ligation PCR amplification)
3. QF-PCR (Quantitative Fluorescent Polymerase
These methods of analysis do not require culturing,
the amount of the sample material may be very small
and the result is obtained in just few days. In compar-
ison, classical cytogenetic analysis (karyotyping) after
amniocentesis requires 15-20 ml of amniotic fluid, cul-
turing of fetal cells (amniocytes) and takes around 10
to 21 days to produce the result [22-26].
New diagnostic standards assume performing clas-
sical cytogenetic analysis in cases of structural fetal
malformations found on ultrasound scan, the presence
of a balanced chromosomal translocation in one of the
parents or chromosomal defects in previous child.
Additionally the use of methods such as FISH, PCR,
MLPA or array-CGH (micro array comparative
genomic hybridization) is suggested, the latter being
especially useful in detecting genomic imbalance in
the fetus (duplications/deletions) [26-30].
The introduction of new diagnostic techniques
requires changes in current standard procedures. The
UK National Screening Committee recommends rou-
tine implementation of RT in pregnancies with high
risk of aneuploidies (21, 13, 18, X and Y). This
approach includes classical cytogenetic analysis only
when there are premises to suspect other than men-
tioned chromosomal aberrations [31-33].
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