Access to this full-text is provided by PLOS.
Content available from PLOS One
This content is subject to copyright.
RESEARCH ARTICLE
An evidence-based definition of anemia for
singleton, uncomplicated pregnancies
Amanda C. ZofkieID
1,2☯
*, W. Holt GarnerID
1‡
, Rachel C. Schell
1‡
, Alexandra
S. RagsdaleID
1‡
, Donald D. McIntireID
1‡
, Scott W. Roberts
1☯
, Catherine Y. Spong
1☯
1Maternal-Fetal Medicine Division, Department of Obstetrics and Gynecology, University of Texas
Southwestern Medical Center, Parkland Health and Hospital System, Dallas, Texas, United States of
America, 2Maternal-Fetal Medicine Division, Department of Obstetrics and Gynecology, Washington
University School of Medicine in St. Louis, St. Louis, Missouri, United States of America
☯These authors contributed equally to this work.
‡ WHG, RCS, ASR and DDM also contributed equally to this work.
*azofkie@gmail.com,zofkie@wustl.edu
Abstract
Background
The definition for anemia in pregnancy is outdated, derived from Scandinavian studies in the
1970’s to 1980’s. To identity women at risk of blood transfusion, a common cause of Severe
Maternal Morbidity, a standard definition of anemia in pregnancy in a modern, healthy
United States cohort is needed.
Objective
To define anemia in pregnancy in a United States population including a large county vs. pri-
vate hospital population using uncomplicated patients.
Materials and methods
Inclusion criteria were healthy women with the first prenatal visit before 20 weeks. Exclusion
criteria included preterm birth, preeclampsia, hypertension, diabetes, short interval preg-
nancy (<18 months), multiple gestation, abruption, and fetal demise. All women had iron for-
tification (Ferrous sulfate 325 mg daily) recommended. The presentation to care and pre-
delivery hematocrits were obtained, and the percentiles determined. A total of 2000 patients
were included, 1000 from the public county hospital and 1000 from the private hospital.
Each cohort had 250 patients in each 2011, 2013, 2015, and 2018. The cohorts were com-
pared for differences in the fifth percentile for each antepartum epoch. Student’s t-test and
chi-squared statistical tests were used for analysis, p-value of �0.05 was considered
significant.
Results
In the public and private populations, 777 and 785 women presented in the first trimester
while 223 and 215 presented in the second. The women at the private hospital were more
likely to be older, Caucasian race, nulliparous, and present earlier to care. The fifth
PLOS ONE
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 1 / 8
a1111111111
a1111111111
a1111111111
a1111111111
a1111111111
OPEN ACCESS
Citation: Zofkie AC, Garner WH, Schell RC,
Ragsdale AS, McIntire DD, Roberts SW, et al.
(2022) An evidence-based definition of anemia for
singleton, uncomplicated pregnancies. PLoS ONE
17(1): e0262436. https://doi.org/10.1371/journal.
pone.0262436
Editor: Mohamed A Yassin, Qatar University,
QATAR
Received: August 10, 2021
Accepted: December 23, 2021
Published: January 13, 2022
Copyright: ©2022 Zofkie et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: The de-identified data
set underlying this study is available in a
Supporting information file.
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
percentile was compared between the women in the private and public hospitals and were
clinically indistinguishable. When combining the cohorts, the fifth percentile for hemoglobin/
hematocrit was 11 g/dL/32.8% in the first trimester, 10.3 g/dL/30.6% in the second trimester,
and 10.0 g/dL/30.2% pre-delivery.
Conclusions
Fifth percentile determinations were made from a combined cohort of normal, uncompli-
cated pregnancies to define anemia in pregnancy. Comparison of two different cohorts con-
firms that the same definition for anemia is appropriate regardless of demographics or
patient mix.
Introduction
Maternal mortality complicated 20.1 per 100,00 live births in 2019 in the United States, a
higher rate than other medically developed countries [1]. As a proxy to mortality, Severe
Maternal Morbidity (SMM) is a set of risk metrics measured to identify these adverse out-
comes, which are often preventable. While the potential morbidities in pregnancy are numer-
ous, the Centers for Disease Control (CDC) has specifically identified the need for blood
transfusion as a leading cause of SMM, an adverse outcome which has increased significantly
in the last two decades [2,3]. As a necessary predictor for the risk of transfusion, and those
women at risk for evaluation and treatment of anemia, an evidence-based definition of anemia
in pregnancy is of paramount importance.
Anemia has been traditionally defined by the CDC and World Health Organization
(WHO) as hemoglobin or hematocrit values less than the fifth percentile of the population in
pregnant and nonpregnant populations [4,5]. In pregnancy, this translates to a hemoglobin of
less than 11 g/dL or a hematocrit less than 33% in the first and third trimesters and a hemoglo-
bin of less than 10.5 g/dL or hematocrit less than 32% in the second trimester, accounting for
the expanded plasma volume of pregnant women [3]. These definitions were originally defined
in 1989 and reaffirmed in 1998 [4,6]. These fifth percentile population values were derived
from four small European studies in pregnant women from the late 1970’s to the 1980’s [7–
10]. These studies examined a total of 427 pregnant women between the four studies. The
American College of Obstetricians and Gynecologists has also supported this definition of ane-
mia in pregnancy [11]. To date, there have been no studies to determine if they are valid in a
modern United States pregnant population.
The normal hematologic changes of pregnancy include an expansion of plasma volume
that exceeds the pregnancy-related increase in red blood cell mass which creates a “physio-
logic anemic state.” This physiologic anemia predisposes women to lower hemoglobin and
hematocrit values during pregnancy. Iron deficiency affects 30–38% of women of childbear-
ing age [12]. Several factors can affect hematocrit values in pregnant women, such as short
interval pregnancy, preeclampsia, race, socioeconomic status, and pre-existing maternal
comorbidities. We sought to define anemia in normal, uncomplicated pregnancies. We gath-
ered data from two cohorts of pregnant women: one cohort at a public county hospital and
another at a private hospital and compared these cohorts to identify if there was a difference
between the fifth percentiles. We hypothesized that there would be no statistical or clinical
difference between the cohorts, and thus combined a definition of anemia in pregnancy
could be established.
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 2 / 8
Materials and methods
To evaluate a time-independent, representative normal, uncomplicated cohort, the first 250
women in 2011, 2013, 2015 and 2018 to deliver at a large inner-city county hospital (Parkland
Health and Hospital Systems) and a private University-Practice hospital (Clements University
Hospital) that met inclusion criteria were studied for a total of 2000 women. Women were
included if they presented to prenatal care before 20 weeks of gestation. Exclusion criteria
included preterm birth (less than 37-weeks gestation), preeclampsia, hypertension, diabetes,
short interval pregnancy (less than 18 months from delivery to conception), multiple gestation,
placental abruption, pyelonephritis during the pregnancy, maternal sickle cell disease, mater-
nal hemoglobinopathies, placenta previa, placenta accreta spectrum, fetal demise, and patients
requiring parenteral iron infusions during the antepartum period. Gestational age at presenta-
tion to care and delivery were obtained on all women. All women had iron fortification with
ferrous sulfate 325 mg daily recommended throughout pregnancy. Presentation to care hemo-
globin/hematocrit, and pre-delivery values were obtained. If hemoglobin (g/dL) levels were
not available, they were derived from the hematocrit levels drawn [13,14]. The fifth percentile
for both hemoglobin and hematocrit was determined from the cohorts and the fifth percentile
was determined for presentation to care, first trimester, second trimester, and pre-delivery.
The cohorts were compared in demographics, hemoglobin/hematocrit values, and their fifth
percentiles. The primary outcome was the difference between fifth percentile values at each
antepartum epoch between the public and private hospital cohorts. This study was deemed
exempt by the Institutional Review Board (IRB) at the University of Texas Southwestern Medi-
cal Center (STU 2020–0200) and the IRB waived the requirement for informed consent. The
data set was not fully anonymized before it was accessed but was anonymized before data
analysis.
After comparison of the cohorts was completed, the two cohorts were combined to create
a diverse patient mixed cohort to use for the definition of anemia in normal, uncomplicated
pregnancies. The fifth percentile of the combined cohort (n = 2000) as a whole was calculated
for each antepartum epoch.
Statistical analysis
Maternal demographics were compared using the student’s t-test or chi-squared test where
appropriate. Fifth percentile values of each antepartum epoch were compared between the
cohorts by estimating the fifth percentiles through the empirical distribution (ordered data
points) by locating the first point in the ordered distribution which is 5% of the way through
the distribution. Estimates of the difference in the fifth percentile between the public and pri-
vate hospital cohorts were estimated using quantile regression with an indicator variable of
hospital location. The estimate of the coefficient was then the estimate of the fifth percentile.
Confidence intervals were presented using the Student’s t-distribution for this estimate. The
null hypothesis of the test is that the coefficient of the indicator variable is equal to zero. This
was then evaluated with the student’s t-test.
Results
Of the 2000 women, there were 1000 from the public and 1000 from the private hospital. Each
cohort of 1000 patients were comprised of the first 250 patients to deliver at each institution in
2011, 2013, 2015, and 2018 that met criteria for inclusion in order to identify women without
complications. To identify a normal, uncomplicated cohort of 1000 women in each cohort,
3567 women were screened with 842 excluded in the public hospital cohort and 725 in the pri-
vate hospital cohort, as per the exclusion criteria (Fig 1). In the public cohort this included 197
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 3 / 8
women in 2011, 182 women in 2013, 208 women in 2015, and 255 women in 2018 in the pub-
lic cohort. The private cohort excluded 388 women in 2011, 72 women in 2013, 116 women in
2015 and 149 women in 2018. Maternal demographics and outcomes of each normal, uncom-
plicated cohort are depicted and compared in Table 1. Those patients in the private hospital
cohort were significantly older, more likely to be nulliparous, and had a higher percentage of
White women when compared to the public hospital cohort, which had a higher percentage of
Hispanic women.
The hematologic indices in each cohort and antepartum epoch are presented and compared
in Table 2. Seven hundred and seventy-seven patients presented in the first trimester (less than
14 weeks gestation) in the public hospital cohort, with 785 in the private cohort. When com-
pared by student’s t-test, the hemoglobin mean in each antepartum epoch and the hematocrit
mean in the second trimester and third trimester/predelivery were statistically different
between the cohorts. The estimates of the fifth percentiles of each antepartum epoch are com-
pared between the public hospital cohort and the private hospital cohort in Table 3. The pre-
delivery hemoglobin and hematocrit fifth percentile estimates were statistically different
between the cohorts.
Fig 1. Flow diagram of anemia cohort distribution.
https://doi.org/10.1371/journal.pone.0262436.g001
Table 1. Maternal demographics and obstetric outcomes.
Characteristic Public Hospital Cohort (n = 1000) Private Hospital Cohort (n = 1000) p-value
Age (years) 27.4±6.2 29.6±5.6 <0.001
Race/Ethnicity <0.001
Hispanic 850 (85) 121 (12)
Black 99 (10) 196 (20)
White 21 (2) 405 (40)
Other 30 (3) 161 (16)
Unknown 0 (0) 117 (12)
Nulliparous 322 (32) 509 (51) <0.001
Gestational Age at Presentation to Care (weeks) 10.4±3.7 10.8±3.4 0.01
Delivery mode 0.46
Vaginal Delivery 692 (69) 707 (71)
Cesarean Section 308 (31) 293 (29)
Data expressed as n (%) or mean ±standard deviation as appropriate. Student’s t-test and Chi-squared tests used where appropriate.
https://doi.org/10.1371/journal.pone.0262436.t001
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 4 / 8
The combined cohort of normal, uncomplicated pregnancies fifth percentiles of each ante-
partum epoch are detailed in Table 4, which can be used to define anemia at each timepoint in
pregnancy.
Conclusions
By comparing the hematologic indices of normal, uncomplicated diverse populations of
obstetric patients at each antepartum epoch, we demonstrate that the definition of maternal
anemia is consistent. Using this combined uncomplicated, normal pregnancy cohort, we iden-
tified normal fifth percentile cutoff values to define anemia in pregnancy. The fifth percentile
hematocrit and hemoglobin cutoff values of 10.7 g/dL or 32.1% at presentation to care, 11.0 g/
dL or 32.8% in the first trimester, 10.3 g/dL or 30.6% in the second trimester, and 10.0 g/dL or
30.2% pre-delivery can be used for normal, uncomplicated pregnancies.
Table 2. Average hemoglobin/hematocrit per antepartum epoch.
Antepartum Epoch Public Hospital Cohort (n = 1000) Private Hospital Cohort (n = 1000) p-value
Presentation to Care N = 1000 N = 1000
Hemoglobin (g/dL) 12.3±0.9 12.4±1.1 0.03
Hematocrit (%) 36.9±2.7 37.0±3.0 0.43
First Trimester N = 777 N = 785
Hemoglobin g/dL) 12.4±0.9 12.6±1.0 <0.001
Hematocrit (%) 37.4±2.6 37.3±2.9 0.47
Second Trimester N = 223 N = 215
Hemoglobin (g/dL) 11.8±0.9 12.1±1.1 0.002
Hematocrit (%) 35.3±2.7 35.9±3.1 0.03
Pre-Delivery N = 1000 N = 1000
Hemoglobin (g/dL) 12.1±1.1 11.9±1.3 <0.001
Hematocrit (%) 36.2±3.2 35.9±3.4 0.04
Data expressed as mean ±standard deviation.
https://doi.org/10.1371/journal.pone.0262436.t002
Table 3. Comparison of fifth percentile estimates between cohorts by antepartum epoch.
Antepartum Epoch Public Hospital Cohort Fifth Percentile Estimate Private Hospital Cohort Fifth Percentile Estimate p-value
Presentation to Care N = 1000 N = 1000
Hemoglobin (g/dL) 10.7 (10.6, 10.9) 10.7 (10.6, 10.9) 0.78
Hematocrit (%) 32.2 (31.8, 32.7) 32.2 (31.4, 32.4) 1.00
First Trimester N = 777 N = 785
Hemoglobin (g/dL) 11.0 (10.9, 11.1) 11.0 (10.8, 11.1) 1.00
Hematocrit (%) 33.0 (32.7, 33.4) 32.5 (32.2, 33.0) 0.09
Second Trimester N = 223 N = 215
Hemoglobin (g/dL) 10.2 (9.7, 10.5) 10.4 (9.6, 10.6) 0.55
Hematocrit (%) 30.6 (29.1, 31.4) 30.8 (28.7, 31.6) 0.83
Pre-Delivery/Third Trimester N = 1000 N = 1000
Hemoglobin (g/dL) 10.2 (10.0, 10.4) 9.6 (9.3, 9.8) <0.001
Hematocrit (%) 30.7 (30.1, 31.1) 29.9 (29.3, 30.4) 0.02
Data presented as Fifth Percentile Estimate (95% Confidence Interval).
https://doi.org/10.1371/journal.pone.0262436.t003
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 5 / 8
The European studies from the 1970’s and 1980’s used iron fortified pregnant women to
obtain their mean and fifth percentile hemoglobin and hematocrits [6–8,15]. In turn, the
CDC adopted these measures as there were no comparable population-based studies in the
United States for normal pregnant women. Our pre-delivery hematocrit in term pregnancies
of 30.2% in our selected “normal” population is less than the recognized 33% from the Centers
for Disease Control. However, the United States population is different and more diverse than
that of Scandinavia, and there have been significant changes in obstetric and medical care
within the past 35 years.
In our data set, there were statistical differences between the hemoglobin mean in each
antepartum epoch and the hematocrit mean in the second trimester and third trimester/prede-
livery between the cohorts. However, it could be argued that these differences are clinically
irrelevant as these differences are within the standard of error.
Anemia can have many different causes and contributing factors to its development and
pathophysiology. To be able to define cutoff values, it is critical to use a normal, healthy and
uncomplicated obstetric population. By defining anemia in pregnancy, we are able to identify
women at risk of severe maternal morbidity and mortality and circumvent the need for blood
transfusion postpartum. Furthermore, this will translate into the timing of interventions such
as iron fortification and other measures to increase hematocrit in pregnancy prior to delivery,
such as parenteral iron or erythropoietin derivatives [16].
Determining women at the highest risk for blood transfusion, a marker for severe maternal
morbidity, is imperative when determining when to intervene in the events surrounding deliv-
ery. Defining a hemoglobin cutoff of 10.0 g/dL and hemoglobin cutoff of 30.2% at delivery to
be the fifth percentile cutoff values will assist labor and delivery clinicians in determining
which patients may be at highest risk for a blood transfusion or severe maternal morbidity sur-
rounding delivery and allow them to prepare by alerting the blood bank or having postpartum
hemorrhage treatments readily available at delivery.
This study determines fifth percentile values to define anemia from a modern, United States
pregnant cohort. Future studies can focus on defining anemia by maternal outcomes, specifi-
cally Severe Maternal Morbidity outcomes and determine if patients who had poor outcomes
had differing values than fifth percentile values from a normal, uncomplicated population.
Future studies also need to focus on interventions that can prevent SMM in anemic popula-
tions prior to delivery.
A strength of our study is that we provide data from a modern United States cohort to
define normative values for anemia. Current recommendations are based on small studies that
were performed in European countries over 35 years ago. In addition, consistent with studies
defining anemia in non-pregnant individuals, we used a normal, healthy population, control-
ling for obstetric and medical complications that could impact the hematologic values at deliv-
ery, which has not been previously described.
One of the main limitations of our study were that our cohort was representative of a
majority white-Hispanic population. Only a minority of our combined population (n = 295 or
15%) was African American, a population in which anemia in pregnancy is prevalent. There is
Table 4. Anemia defined, fifth percentile values of a normal, uncomplicated population.
Antepartum Epoch Hemoglobin (g/dL) Hematocrit (%)
Presentation to Care 10.7 32.1
First Trimester 11.0 32.8
Second Trimester 10.3 30.6
Pre-Delivery/Third Trimester 10.0 30.2
https://doi.org/10.1371/journal.pone.0262436.t004
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 6 / 8
support, however, for equivalent iron stores (higher ferritin levels in African American men
and women) between Caucasian and African American women [17,18]. At our public hospital
system, we primarily utilize hematocrits because of the nature of our hospital and prenatal
care clinic system. Hematocrits, not complete blood counts, are often obtained in our prenatal
clinicals and labor and delivery area due to this reason. However, hematocrit and hemoglobin
are equivalent measures in most patients, and the equivalent values can be estimated from
each other with clinical accuracy [13,14]. It is also acknowledged that some women in our
overall cohort may have underlying iron deficiency anemia or an unknown diagnosis of thalas-
semia that may skew the results. This could not be clarified in our data set as not all women
had iron, ferritin, or mean corpuscular volume drawn during their routine pregnancy labora-
tory studies. Finally, while iron fortification was recommended for all women, compliance
remains a limitation. we were not able to evaluate if each patient was compliant with the
recommendation.
These data provide guidance for practitioners defining anemia in a United States popula-
tion as hematocrit and hemoglobin values of 32.1% or 10.7 g/dL at presentation to care, 32.8%
or 11.0 g/dL in the first trimester, 30.6% or 10.3 g/dL second trimester, and 30.2% or 10.0 g/dL
pre-delivery. These data will be essential for risk stratification for postpartum hemorrhage,
blood transfusion, and understanding severe maternal mortality indicators. With a standard,
contemporary definition, an approach to mitigate anemia at delivery and improve pregnancy
outcomes is possible.
Supporting information
S1 Data.
(XLSX)
Acknowledgments
We thank the obstetric patients at Parkland Health and Hospital Systems and Clements Uni-
versity Hospital.
Author Contributions
Conceptualization: Amanda C. Zofkie, Scott W. Roberts, Catherine Y. Spong.
Data curation: Amanda C. Zofkie, W. Holt Garner, Rachel C. Schell, Alexandra S. Ragsdale,
Donald D. McIntire, Scott W. Roberts, Catherine Y. Spong.
Formal analysis: Amanda C. Zofkie, Donald D. McIntire, Scott W. Roberts, Catherine Y.
Spong.
Investigation: Amanda C. Zofkie, Scott W. Roberts, Catherine Y. Spong.
Methodology: Amanda C. Zofkie.
Project administration: Amanda C. Zofkie, Catherine Y. Spong.
Resources: Catherine Y. Spong.
Supervision: Amanda C. Zofkie, Scott W. Roberts, Catherine Y. Spong.
Validation: Amanda C. Zofkie, Scott W. Roberts, Catherine Y. Spong.
Writing – original draft: Amanda C. Zofkie, W. Holt Garner, Rachel C. Schell, Alexandra S.
Ragsdale, Scott W. Roberts, Catherine Y. Spong.
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 7 / 8
Writing – review & editing: Amanda C. Zofkie, W. Holt Garner, Rachel C. Schell, Alexandra
S. Ragsdale, Scott W. Roberts, Catherine Y. Spong.
References
1. Hoyert DL. Maternal mortality rates in the United States, 2019. NCHS Health E-Stats [Internet]. 2021
Apr [cited 2021 Jul 22]; [about 5 p.] https://www.cdc.gov/nchs/data/hestat/maternal-mortality-2021/E-
Stat-Maternal-Mortality-Rates-H.pdf.
2. Kilpatrick SK, Ecker JL. Severe maternal morbidity: screening and review. Am J Obstet Gynecol. 2016;
215(3):B17–22. https://doi.org/10.1016/j.ajog.2016.07.050 PMID: 27560600
3. Callaghan WM, Creanga AA, Kuklina EV. Severe maternal morbidity among delivery and postpartum
hospitalizations in the United States. Obstet Gynecol. 2012; 120(5):1029–1036. https://doi.org/10.
1097/aog.0b013e31826d60c5 PMID: 23090519
4. Recommendations to prevent and control iron deficiency in the United States. Centers for Disease Con-
trol and Prevention. MMWR Recomm Rep. 1998; 47(Rr-3):1–29. PMID: 9563847
5. WHO Guidelines Approved by the Guidelines Review Committee. In: WHO Recommendations on Ante-
natal Care for a Positive Pregnancy Experience. Geneva: World Health Organization 2016.; 2016.
6. CDC criteria for anemia in children and childbearing-aged women. MMWR Morb Mortal Wkly Rep.
1989; 38(22):400–404. PMID: 2542755
7. Svanberg B, Arvidsson B, Norrby A, Rybo G, Solvell L. Absorption of supplemental iron during preg-
nancy—a longitudinal study with repeated bone-marrow studies and absorption measurements. Acta
Obstet Gynecol Scand Suppl. 1975; 48:87–108. https://doi.org/10.3109/00016347509156332 PMID:
1062910
8. Sjostedt JE, Manner P, Nummi S, Ekenved G. Oral Iron Prophylaxis During Pregnancy–A Comparative
Study on Different Dosage Regimens. Acta Obstet Gynecol Scand. 1977; 56(S60):3–9. https://doi.org/
10.1111/aogs.1977.56.s60.3 PMID: 29120032
9. Puolakka J, Janne O, Pakarinen A, Jarvinen PA, Vihko R. Serum ferritin as a measure of iron stores
during and after normal pregnancy with and without iron supplements. Acta Obstet Gynecol Scand
Suppl. 1980; 95:43–51. https://doi.org/10.3109/00016348009156379 PMID: 6935911
10. Taylor DJ, Mallen C, McDougall N, Lind T. Effect of iron supplementation on serum ferritin levels during
and after pregnancy. Br J Obstet Gynaecol. 1982; 89(12):1011–1017. https://doi.org/10.1111/j.1471-
0528.1982.tb04656.x PMID: 7171510
11. ACOG Practice Bulletin No. 95: anemia in pregnancy. Obstet Gynecol. 2008; 112(1):201–207. https://
doi.org/10.1097/AOG.0b013e3181809c0d PMID: 18591330
12. Camaschella C. Iron-deficiencyanemia, N Engl J Med. 2015; 372(19):1832–1843. https://doi.org/10.
1056/NEJMra1401038 PMID: 25946282
13. Weatherall MS, Sherry KM. An evaluation of the Spuncrit infra-red analyser for measurement of haema-
tocrit. Clin Lab Haematol. 1997; 19(3):183–186. PMID: 9352142
14. Nijboer JMM, van der Horst ICC, Hendriks HGD, ten Duis HJ, Mifsten MWN. Myth or reality: hematocrit
and hemoglobin differ in trauma. J Trauma. 2007; 62(5):1310–2. https://doi.org/10.1097/TA.
0b013e3180341f54 PMID: 17495743
15. World Health Organization. (2001). The Clinical use of blood in medicine, obstetrics, paediatrics, sur-
gery and anaesthesia, trauma and burns. Geneva: World Health Organization, Blood Transfusion
Safety. https://apps.who.int/iris/handle/10665/42397.
16. Sienas L, Wong T, Collins R, Smith J. Contemporary uses of erythropoietin in pregnancy: a literature
review. Obstet Gynecol Surv. 2013; 68(8):594–602. https://doi.org/10.1097/OGX.0b013e3182a2d51c
PMID: 23921673
17. Johnson_Spear MA, Yip R. Hemoglobin difference between black and white women comparable iron
status: justification for race-specific anemia criteria. Am J Clin Nutr 1994; 60:117–21. https://doi.org/10.
1093/ajcn/60.1.117 PMID: 8017324
18. Perry GS, Byers T, Yip R, Margen S. Iron nutrition does not account for the hemoglobin differences
between blacks and whites. J Nutr 1992; 122:1417–24. https://doi.org/10.1093/jn/122.7.1417 PMID:
1619469
PLOS ONE
Defining anemia in pregnancy
PLOS ONE | https://doi.org/10.1371/journal.pone.0262436 January 13, 2022 8 / 8
Available via license: CC BY 4.0
Content may be subject to copyright.