The Journal of Nutrition
Dietary Supplement Use and Folate Status
during Pregnancy in the United States1
Amy M. Branum,2,5* Regan Bailey,3and Barbara J. Singer4
2National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD;3Office of Dietary Supplements,
National Institutes of Health, Bethesda, MD; and4University of Maryland, School of Public Health, Department of Family Science
Adequatefolateandiron intakeduringpregnancyiscriticalformaternalandfetalhealth.Nopreviousstudiestoour knowledge
have reported dietary supplement use and folate status among pregnant women sampled in NHANES, a nationally repre-
sentative, cross-sectional survey. We analyzed data on 1296 pregnant women who participated in NHANES from 1999 to
2006 to characterize overall supplement use, iron and folic acid use, and RBC folate status. The majority of pregnant women
(77%) reported use of a supplement in the previous 30 d, most frequently a multivitamin/-mineral containing folic acid (mean
817 mg/d) and iron (48 mg/d). Approximately 55–60% of women in their first trimester reported taking a folic acid- or iron-
containing supplement compared with 76–78% in their second trimester and 89% in their third trimester. RBC folate was
lowest inthefirst trimester anddiffered bysupplementuseacrossall trimesters.MedianRBC folatewas1628nmol/L among
users and 1041 nmol/L among nonusers. Among all pregnant women, median RBC folate increased with trimester (1256
nmol/L in the first, 1527 nmol/L in the second, and 1773 nmol/L in the third). Given the role of folic acid in the prevention of
neural tube defects, it is notable that supplement use and median RBC folate was lowest in the first trimester of pregnancy,
with 55% of women taking a supplement containing folic acid. Future research is needed to determine the reasons for low
compliance with supplement recommendations, particularly folic acid, in early pregnancy.J. Nutr. 143: 486–492, 2013.
Micronutrient needs increase during pregnancy due to changes
in physiology and homeostatic control (1,2). Although increased
nutrient intake should preferably come from food sources, even
within the developed world it may be unlikely that pregnant and
child-bearing–age women meet their needs for micronutrients,
such as iron and calcium, through foods alone (2,3). However,
the extent of potential nutrient deficiency during pregnancy may
vary by demographic characteristics, such as younger maternal
age and lower income and education (1,4). Although general
multivitamin supplement use during pregnancy is not formally
recommended, clinicians routinely recommend or prescribe pre-
natal vitamins to potentially compensate for dietary shortfalls
(5). However, supplementation with folic acid and iron specif-
ically, either before or during pregnancy, is recommended by
several health organizations (1,4–8). In addition to supplemen-
tation, the U.S. food supply was fortified with folic acid be-
ginning in 1997 to target reproductive-aged females in order to
reduce the incidence of neural tube defects (9). Despite this
fortification, women of child-bearing age still have usual folic
acid intakes below the recommendations (10,11).
Although prenatal vitamin and mineral supplements are
widely recommended as a standard of care in clinical practice,
little is known about the national prevalence of supplement use
during pregnancy and the characteristics of pregnant women
who take dietary supplements. In addition, folic acid and iron
supplement use and folate status have not, to our knowledge,
been examined among a nationally representative sample of
pregnant women in the US. Previous studies of dietary supple-
ment use in pregnancy using national data are now outdated
because of changes in folic acid awareness and fortification
(12,13), are specific to only one micronutrient (14), or are not
specific beyond multivitamin use (15). Therefore, the purpose of
this analysis is to describe the prevalence and correlates of die-
tary supplement use as well as iron and folic acid supplement use
and to describe RBC folate status during pregnancy using data
from the NHANES (1999–2006).
Subjects and Methods
We used data from the 1999–2006 NHANES for this analysis.
NHANES is a nationally representative, cross-sectional sample of the
U.S. civilian, noninstitutionalized population administered by the
National Center for Health Statistics (16). Since 1999, NHANES has
been operated as a continuoussurvey and includes a household interview
component followed by a physical examination in the mobile examina-
tion center(MEC)6. Duringthe 1999–2006NHANES,responserates for
1Author disclosures: A. M. Branum, R. Bailey, and B. J. Singer, no conflicts of
interest. The findings and conclusions in this paper are those of the authors and
do not necessarily represent the views of the National Center for Health
Statistics, CDC, or the Office of Dietary Supplements or the NIH.
5Present address: National Center for Health Statistics, Office of Analysis and
Epidemiology, 3311 Toledo Rd, Room 6113, Hyattsville, MD 20782.
* To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
6Abbreviations used: MEC, mobile examination center; PIR, poverty income
ratio; RHQ, reproductive history questionnaire.
ã 2013 American Society for Nutrition.
Manuscript received September 21, 2012. Initial review completed November 2, 2012. Revision accepted December 28, 2012.
First published online January 30, 2013; doi:10.3945/jn.112.169987.
by guest on December 28, 2015
the household interview averaged 81% and averaged 77% for the MEC
exam.Duringthissame period,NHANESoversampled pregnantwomen
(17). This analysis of secondary data was not subject to institutional
review by any of the participating organizations.
Pregnancy status for NHANES participants is assessed during both
the household interview and the MEC examination. In addition to being
asked about current pregnancy status at the time of the household
screening,women ages 8–59y whowere examined in the MEC were also
given a urine pregnancy test before undergoing an examination (17).
Only women who were seen in the MEC were included in this analysis.
In addition, questions about currently being pregnant and month of
pregnancy were asked during the MEC examination as part of the re-
productive health questionnaire (RHQ) (18). From 1999 to 2006, we
initially identified 1274 women who were pregnant at the time of their
MEC participation according to the RIDEXPRG variable, which
indicates pregnancy status in NHANES. Twenty-two additional women
had a missing pregnancy status according to the RIDEXPRG variable
but stated they were currently pregnant and had information on month
of pregnancy in the RHQ. We therefore reassigned their status to
‘‘pregnant,’’ resulting in 1296 pregnant women available for analysis. Of
these, all women had data on dietary supplement use.
Supplement use, folate status, and covariates. Dietary supplement
use was assessed as part of the household interview for all NHANES
participants. Survey participants were asked to complete the dietary
supplement questionnaire that examines use of dietary supplements in
the previous 30 d. If a person reported use of supplements, they were
asked to provide the container and/or label of the products, which
were then quantified and verified by survey personnel through ex-
amination of the supplement labels or by otherwise obtaining in-
formation from the supplement manufacturers (19). In the NHANES
dietary supplement data, antacid use is considered separately from
other dietary supplement use. If a pregnant woman answered ‘‘no’’ to
the question regarding dietary supplement use but ‘‘yes’’ to the ques-
tion on antacid use, she was not counted in this analysis as a dietary
supplement user. This was done to avoid over-representing true dietary
supplement use by including women who might have used antacids
only for medicinal purposes (e.g., to relieve heartburn) instead of to
obtain minerals such as calcium and magnesium, which antacids com-
monly contain. Because of this, if a pregnant respondent answered
‘‘yes’’ to the dietary supplement question and reported taking antacids
in addition to other supplements, the antacids were included and
analyzed as their own group to distinguish them from other mineral
For the more general analysis on supplement intake, we classified
supplements according to the following categories: 1) combined
multivitamin/-mineral: supplement containing mainly both vitamins and
minerals; 2) single or multivitamin: supplement contains one or more
vitamins with no minerals; 3) single or multimineral: supplement con-
tains one or more minerals with no vitamins and is not otherwise clas-
sified as an antacid; 4) botanical/herbal/other: supplement contains
mainlybotanicalor other non-vitamin or mineralingredients; 5) antacid:
supplement may contain multiple minerals but is classified as an antacid;
and 6) unknown: supplement reported but name and ingredients were
unknown. The categories of herbal/botanical/other and unknown had
too few reported to make reliable estimates and therefore results are not
shown.Forthe specificfolicacid andiron supplement intakeanalysis,we
identified supplements by their inclusion of folic acid or iron as noted by
their respective ingredient identification codes on the appropriate dietary
supplement analytic file.
We examined RBC folate (nmol/L), which is collected and analyzed
as part of the standard venipuncture performed during the MEC ex-
amination (20). For all the years included in this analysis, we measured
serum and RBC folate using the Bio-Rad Laboratories assay; however, it
has been shown that this assay underestimates RBC folate when com-
pared to the gold-standard microbiological assay (21). Therefore, we
adjusted RBC folate values using regression equations as recommended
by the National Center for Health Statistics (22). Data on RBC folate
were missing for 92 (7.1%) of pregnant women. We examined only RBC
folate in this analysis, because it is a better indicator of long-term folate
storage than serum folate and not subject to hemodilution that occurs
during pregnancy (23).
Covariates of interest included age (<25, $25 y), race/ethnicity (non-
Hispanic white, non-Hispanic black, Mexican-American, and other,
including other Hispanic), marital status (married or unmarried),
education (high school graduate or less, some college or more), parity
(first pregnancy or second or greater pregnancy), trimester of pregnancy
coded according to the month of pregnancy reported by the respondent
on the RHQ, health insurance coverage status, and socioeconomic
status. Socioeconomic status was assessed using poverty income ratio
(PIR), which is the ratio of income to the appropriate poverty threshold,
developed and updated regularly by the U.S. Census Bureau (24). A ratio
of <1 designates a family or individual as being ‘‘poor’’ or falling below
the federal poverty threshold. For the current analysis, the PIR was
categorized as poor (<1), near-poor (1 to <2), and not poor ($2).
Statistical analysis. Weighted frequencies of the socio-demographic
characteristics were examined for pregnant women taking and not
taking supplements. Percentages and SEs were estimated using PROC
DESCRIPTin SUDAAN (25). We present results in text as percentages 6
SE. Significant differences in percentages within variable categories were
assessed using pairwise comparisons generated by the PRED_EFF state-
ment in PROC RLOGISTat the P < 0.05 level (25). Because supplement
use was highly prevalent in these data, resulting in ORs substantially
higher than the RR, we calculated model-adjusted prevalence ratios and
95% CIs for each covariate using the PREDMARG statement in PROC
RLOGIST (26). Model-adjusted methods were used to further examine
these associations after adjusting for the effect of the other variables and
determining the most parsimonious model. The logistic regression
models do not include missing data. We also estimated the percent of
pregnant women reporting dietary supplement use according to the
broader categories of supplements and specifically folic acid and iron
using PROC SURVEYFREQ in SAS (27). The mean intake of folic acid
and iron intake via dietary supplements (mean 6 SE) was calculated
using an algorithm and program provided by National Center for Health
Statistics (28). Mean and percentiles of RBC folate were estimated
according to supplement use and trimester of pregnancy using PROC
DESCRIPT. All results were weighted using the MEC examination
weights, which were combined and recalculated for all years of
NHANES used in analysis per NHANES guidance (29).
Of pregnant women, 78% 6 2 reported supplement use in the
previous 30 d (Table 1). Pregnant women using supplements
differed from women not using supplements by nearly every
characteristic. Compared with those not taking supplements,
pregnant women reporting supplement use were more likely to
be 25 y of age or older, have at least some college education, and
were more likely to be non-Hispanic white. Eighteen percent of
supplement users were unmarried compared with 47% among
supplement nonusers. Pregnant women who reported supple-
ment use were more likely to be in their third trimester, whereas
women reporting no supplement use were more likely in their
first trimester. Whereas most supplement users and nonusers had
some type of health insurance, nonusers were more likely to be
uninsured than women who reported supplement use. Finally,
pregnant women reporting supplement use were more likely to
have a PIR of $2 (indicating higher income) compared with
those not taking supplements.
In the crude bivariate analysis (Table 2), significant associ-
ations supported the results shown in Table 1. Due to the cor-
relation among education, income, and health insurance, only
education was included in the adjusted model, along with the
other demographic characteristics. Education was selected due
to its previously shown association with nutritional habits (30).
Health insurance was then added to this model to assess whether
Dietary supplement use among pregnant women487
by guest on December 28, 2015
it had an additional impact on the correlates of supplement use;
however, addition of insurance did not change the model fit or
substantially alter the associations with the other correlates. The
results of that model are shown in Table 2. Addition of income
did not change model fit and is not presented here. After ad-
justing for all variables, except income, only trimester and edu-
cation were significantly associated with supplement use.
The majority of pregnant women reported taking a
multivitamin/mineral (Table 3). In addition, 74% reported tak-
ing a supplement, either a multivitamin or multimineral con-
taining folic acid, and 73% reported taking an iron-containing
supplement. Most pregnant women reporting supplement use
reported taking only one supplement (72% 6 3), but values
ranged from 1 to 12 with a mean of 1.4 6 0.1. We examined and
compared the characteristics of women reporting folic acid and
iron supplementation with those not reporting use, but the re-
sults were very similar to those of supplement use overall and are
not reported here.
Finally, we examined the percent of women taking iron and
folic acid by trimester of pregnancy (Table 4) and percentiles of
RBC folate by supplement use and trimester (Table 5). Approx-
imately 55–60% of women in their first trimester reported
taking a folic acid- or iron-containing supplement compared
with 76–78% in their second trimester and 89% in their third
trimester. In general, RBC folate was lower among supplement
nonusers and lowest among women in their first trimester.
The majority of pregnant women in the US are using a dietary
supplement at some time during their pregnancy, most fre-
quently a multivitamin/-mineral product. However, ~20% re-
ported not using a dietary supplement during pregnancy,
although this may vary by trimester; women in their third tri-
mester of pregnancy were more likely to report using supple-
ments compared with women in their first trimester. In addition,
Characteristics of supplement users and nonusers among pregnant women in NHANES
Supplement users, n = 1007 Supplement nonusers, n = 289 Chi-square P value
n weighted %
77.6 6 2.2
n weighted %
22.4 6 2.2All pregnant women
Second birth or higher
High school or less
Some college or more
28.3 6 2.7
71.7 6 2.7
56.7 6 5.3
43.2 6 5.3
62.5 6 2.7
12.3 6 1.5
11.7 6 1.4
13.5 6 2.3
27.7 6 5.7
27.0 6 4.6
23.6 6 3.7
21.7 6 6.4
17.9 6 2.5
76.0 6 2.9
46.5 6 5.2
45.3 6 4.7
29.5 6 2.7
63.2 6 3.3
17.0 6 4.1
69.5 6 5.6
16.3 6 2.2
34.7 6 3.2
32.9 6 3.1
16.1 6 2.6
44.4 6 6.1
40.8 6 5.3
14.8 6 3.7
25.7 6 4.4
9.4 6 1.4
90.5 6 1.4
34.8 6 4.3
63.8 6 4.5
15.2 6 1.6
16.5 6 2.4
59.4 6 3.4
41.4 6 6.7
21.2 6 4.9
29.1 6 5.9
33.9 6 2.9
66.0 6 2.9
75.5 6 4.5
24.5 6 4.5
1Values are percentage 6 SE based on weighted data.
2Missing denotes women who were missing data for the variable of interest.
3Denote unreliable estimates.
4P value $ 0.05.
488Branum et al.
by guest on December 28, 2015
use of supplements in pregnancy was related to education, in-
come, health insurance status, age, race/ethnicity, and marital
status similar to findings in other life-stage groups and other re-
ports (15,17). However, after multivariate adjustment, only edu-
cation and trimester of pregnancy were significantly associated
with supplement use during pregnancy in the US. We also found
that the majority of pregnant women were taking a supplement
containing folic acid and/or iron and that supplement use was as-
sociated with improved RBC folate status. Finally, RBC folate sta-
tus varied by trimester, indicating potential shortfalls in folic acid
of folic acid use in pregnancy and fortification of the food supply.
To our knowledge, only one previous study has examined
iron supplement use among a nationally representative sample
of pregnant women in the US. Using NHANES III (1988–1994),
Cogswell et al. (14) reported that 72% of pregnant women
sampled reported taking a dietary supplement containing iron.
Although the unweighted sample size (n = 295) was less than in
the current study, our results of 73% closely match. However,
this may indicate that iron supplementation has not improved
among pregnant women in the US in the last decade. In addi-
tion, we report a lower mean intake of iron from supplements
(48 mg/d) compared with the 78 mg/d that Cogswell et al. (14)
reported. The reason for this difference is not clear, although the
estimates from the current study are more closely aligned with
the Tolerable Upper Intake Limit for iron of 45 mg/d (31).
A recent analysis using the same NHANES sample as the current
study reported that the overall prevalence of iron deficiency was
18% among pregnant women, which still exceeds the Healthy
People 2010 baseline measure of 16% and the target goal of
14.5% iron deficiency during pregnancy (32,33). This indicates
that more strides may need to be made to improve iron supple-
mentation to help reduce iron deficiency during pregnancy.
We are not aware of any other study that reported findings
on the prevalence of folic acid supplementation or folate status
among a nationally representative sample of pregnant women in
the US, although studies have reported on folate status and folic
acid intake among nonpregnant women using NHANES data
(11,34,35). An analysis of women of childbearing age sampled
in the 2001–2002 NHANES revealed low intake of folic acid via
supplementation (26%of women 15–49 y old taking >400 mg/d)
(11). Similarly, an analysis of folic acid intake from supplements
and foods from the 2003–2006 NHANES demonstrated that
only 24% of nonpregnant women overall consumed the re-
commended 400 mg/d (34); however, when stratified by supple-
ment use, 72% of women reporting supplement use were found
to consume 400 mg/d folic acid, thus illustrating the role sup-
plements play in helping women obtain the recommended daily
amount. In addition, studies have shown that dietary sup-
plement users have better dietary quality, including higher fruit
and vegetable consumption, and have higher folic acid intakes
from food alone compared with supplement nonusers (36,37);
therefore, the pregnant women reporting supplement use in this
sample could also be obtaining the recommended amount of
folic acid due to improved diets as well. Although we did not
assess dietary intake of this group of pregnant women, future
research could determine if there are differences in dietary
quality associated with supplement use during pregnancy.
Our results also demonstrate that folic acid supplement use
was associated with improved folate status, similar to a recent
population-based study of Canadian women (38). In that study,
Colapinto et al. (39) reported that for supplement nonusers, at
least 25% of pregnant women did not have RBC folate con-
centrations >906 nmol/L, which is one cutoff value that has been
defined to prevent neural tube defects. Our results showed that
among all pregnant women, the 25th percentile value of 953
nmol/L for women in their first trimester was not much above
this particular cutoff value. We found that the RBC folate
concentration was lowest during the first trimester, a time when
supplements and crude and adjusted prevalence ratios for the
association between characteristics and supplement use in
Percentages of pregnant women taking dietary
Second pregnancy or more
High school or less
Some college or more
63.3 6 4.5
85.1 6 2.4
1.34 (1.15, 1.57)1.10 (0.97, 1.24)
88.6 6 2.2
61.2 6 4.1
63.1 6 4.2
68.3 6 7.0
0.69 (0.60, 0.79)
0.71 (0.62, 0.82)
0.77 (0.62, 0.95)
0.86 (0.73, 1.01)
0.90 (0.78, 1.02)
0.82 (0.66, 1.02)
57.0 6 4.4
85.3 6 1.9
1.50 (1.27, 1.76)1.11 (1.00, 1.24)
85.7 6 3.2
75.9 6 3.2
0.89 (0.79, 1.00) 0.93 (0.85, 1.02)
63.0 6 6.7
79.8 6 3.5
91.3 6 2.2
1.27 (1.01, 1.59)
1.45 (1.16, 1.82)
1.16 (0.99, 1.35)
1.30 (1.11, 1.51)
48.3 6 4.8
83.0 6 2.2
1.72 (1.41, 2.09)1.11 (0.95, 1.30)
56.0 6 6.0
72.9 6 5.6
87.6 6 2.8
1.30 (0.97, 1.75)
1.56 (1.25, 1.96)
60.8 6 3.7
90.3 6 2.1
1.48 (1.31, 1.69)1.17 (1.05, 1.30)
1Values are percentage 6 SE and PR (95% CI) based on weighted data. Ref,
2Variable not in adjusted model.
by supplement type and intakes of folic acid and iron supple-
mentation among pregnant women in NHANES 1999–20061
Percentage of pregnant women taking supplements
Unweighted n Value
Any folic acid-containing supplement, %
Any iron-containing supplement, %
Single vitamin, %
Single mineral, %
Supplemental folic acid intake, mg/d
Supplemental iron intake,2mg/d
73.9 6 2.6
72.5 6 2.5
8.4 6 1.5
11.1 6 1.6
74.7 6 2.4
28.4 6 2.4
817 6 27.6
47.7 6 4.2
1Values are percentage 6 SE or mean 6 SE based on weighted data.
2Represents intakes from dietary supplements only.
Dietary supplement use among pregnant women 489
by guest on December 28, 2015
folic acid is critical; however, the median RBC folate in the first
trimester was still greater among the pregnant supplement takers
in our study compared with nonpregnant women ages 15–44 y
from NHANES 1999–2010 as reported by Pfeiffer et al. (40). In
addition, the majority of folic acid supplements reported in this
analysis contained higher dosages of folic acid ($800 mg), which
indicates that most women were taking prenatal doses of folic
acid rather than the lower standard multivitamin dosages (400
mg). Small numbers did not permit us to conduct a more formal
analysis by folic acid dose by trimester. Although we report a
mean daily folic acid intake from supplements of double the
recommended amount and that 72% of pregnant women re-
ported taking a folic-acid supplement, we were not able to assess
when women began using folic acid. However, folic acid sup-
plementation, as well as overall dietary supplement use, was
lowest in the first trimester of pregnancy, a finding not explained
by sociodemographic characteristics.
Although multivitamin and folic acid supplementation is
recommended during early pregnancy, these findings could
reflect the difficulties some women encounter with tolerance of
supplementation, particularly iron supplements, due to nausea
and vomiting in early pregnancy (41,42). In addition, it is pos-
sible that women who were sampled while in their first trimester
may have recently become aware of their pregnancy and there-
fore were not taking supplements. However, because folic acid is
recommended prior to pregnancy for women of child-bearing
age, this may also corroborate the low compliance of these re-
commendations as reported by Yang et al. (11). More research is
needed on the potential for lower-than-recommended nutrient
intakes, particularly in early pregnancy, and to determine the
reasons for noncompliance in early pregnancy.
It is important to note, however, that the pregnant women
in NHANES were not evenly distributed by trimester. Of the
women with data on month of current pregnancy (81% of
women coded as pregnant), 20% were in the first trimester, with
41 and 38% in the second and third trimesters, respectively
(unweighted and weighted data yielded similar distributions).
Women who were missing data on trimester were similar to all
pregnant women in NHANES, with respect to race/ethnicity,
education, and marital status, and ~72% of women missing in-
formation on trimester reported taking supplements; however, it
is possible that some bias may have been incurred by this un-
equal distribution of pregnancy by trimester. We did perform a
sensitivity analysis to try to assess this potential bias where all
pregnant women missing information on month of pregnancy
were reassigned to the first trimester group and the data were
reanalyzed. Although this resulted in a more even distribution of
women by trimester among supplement users, it did not change
the results of the percent of pregnant women taking supplements
by trimester or the logistic regression.
In the current study, education was associated with supple-
ment use in pregnancy, which is similar to findings from studies
of multivitamin use in the general population using NHANES
data (43,44). In addition, education as well as age and race/
ethnicity is associated with intention to be become pregnant,
which in turn is associated with multivitamin and folic acid use
(45,46). Though this could help explain the findings related to
education, information on intention of pregnancy is not avail-
able in NHANES. Further research is needed to understand
potential interactions between intention of pregnancy and
demographic characteristics as they relate to multivitamin
and dietary supplement use.
Our study relies upon self-reported interview data; however,
NHANES interviewers ask to see the dietary supplement con-
tainers that each participant reports using to verify the reported
supplements. Furthermore, although we had a nationally repre-
sentative sample, the unweighted sample sizes were too small to
perform more stratified analyses by supplement type and ex-
amine potential interactions (e.g., race/ethnicity by education).
We were not able to assess other potential factors related to
dietary supplement use in pregnancy, such as pregnancy in-
tention. Furthermore, physiological changes in pregnancy may
alter RBC folate concentrations. With these caveats in mind, the
strengths of our study should not be overlooked. This study
documents supplement use and is the first to our knowledge to
examine folate status in pregnancy in a nationally representative
population of pregnant women who were sampled at different
times throughout pregnancy. The detailed information on sup-
plement use allowed us to explore dietary supplements beyond
multivitamins and minerals among a nationally representative
group of pregnant women, which to the best of our knowledge,
has not been previously done.
containing supplement by trimester of pregnancy in NHANES
Percent of pregnant women taking a folic acid or iron-
Trimester Unweighted nIronFolic acid
56.1 6 6.7
76.4 6 3.8
89.9 6 2.3
56.4 6 6.4
60.0 6 7.0
78.8 6 3.5
89.2 6 2.5
56.5 6 6.4
1Values are percentage 6 SE based on weighted data.
2Missing denotes women who were missing information on month of pregnancy.
women in NHANES 1999–20061
Percentiles of RBC folate by supplement use and trimester of pregnancy among pregnant
RBC folate percentile
10th 25th50th 75th90th
1002 (887, 1111)
622 (547, 792)
808 (725, 900)
1015 (884, 1124)
1146 (1079, 1331) 1467 (1400, 1600) 1773 (1694, 2012) 2159 (2019, 2301) 2536 (2297, 3815)
1360 (1257, 1442) 1628 (1589, 1695) 1968 (1849, 2096) 2420 (2226, 2968)
855 (704, 950)1041 (962, 1184)
953 (904, 1109)1255 (1048, 1525) 1632 (1447, 1916) 2051 (1631, 2412)
1231 (1167, 1366) 1527 (1449, 1630) 1781 (1656, 1990) 2253 (1956, 2603)
1359 (1191, 1540) 1905 (1521, 2590)
1Percentile value (95% CI) based on weighted data.
2Unweighted sample size of pregnant women with measured RBC folate.
3Includes both supplement users and nonusers.
490Branum et al.
by guest on December 28, 2015
Although the majority of U.S. pregnant women appear to be
taking a dietary supplement during pregnancy, ~20% are not.
While young women, those of race/ethnicity other than non-
Hispanic white, and/or those who have less education are at
potential risk for nutritional deficiencies in pregnancy, more re-
search is needed to understand why supplement use may still be
low in early pregnancy. In addition, the results of this analysis
suggest that the desired compliance with folic acid supplement
recommendations for women of child-bearing age are still not
being fully met, as indicated by relatively low RBC folate status
of women in early pregnancy.
A.M.B., R.B., and B.J.S. all contributed to the concept develop-
ment; A.M.B. and B.J.S. analyzed data; A.M.B., R.B., and B.J.S.
contributed to writing of the paper; and A.M.B. had primary
responsibility for the final content. All authors read and approved
the final manuscript.
1. Institute of Medicine. Subcommittee on Nutritional Status and Weight
Gain during, Pregnancy. Nutrition during pregnancy. Part I: weight
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