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International Journal of Epidemiology logoLink to International Journal of Epidemiology
. 2020 Nov 24;50(1):165–178. doi: 10.1093/ije/dyaa200

Vegetarian diets during pregnancy, and maternal and neonatal outcomes

Samrawit F Yisahak 1, Stefanie N Hinkle 2, Sunni L Mumford 2, Mengying Li 2, Victoria C Andriessen 2, Katherine L Grantz 2, Cuilin Zhang 2, Jagteshwar Grewal 1,✉
PMCID: PMC7938506  PMID: 33232446

Abstract

Background

Vegetarian diets are becoming increasingly popular in the USA. Limited research has examined the health consequences of vegetarian diets during pregnancy. We comprehensively examined associations of vegetarianism during pregnancy with maternal and neonatal outcomes.

Methods

We used data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development’s Fetal Growth Studies–Singletons, a prospective multi-site cohort of 1948 low-risk pregnant women of four races/ethnicities (White, Black, Hispanic, Asian/Pacific Islander) in the USA (2009–2013). Vegetarianism was self-reported and also defined based on dietary patterns measured using a self-administered first-trimester food-frequency questionnaire (full [lacto-ovo and vegan], pesco-, semi- and non-vegetarians). Neonatal outcomes included birthweight and neonatal anthropometric measures, small for gestational age, small for gestational age with neonatal morbidity and preterm delivery. Maternal outcomes included gestational weight gain, gestational diabetes, hypertensive disorders of pregnancy and gestational anaemia.

Results

Ninety-nine (6.2%) women self-reported being vegetarian. The diet-based definition identified 32 (2.0%) full vegetarians, 7 (0.6%) pesco-vegetarians and 301 (17.6%) semi-vegetarians. Neonates of diet-based full vegetarians had higher odds of being small for gestational age [adjusted odds ratio (ORadj) = 2.51, 95% confidence interval: 1.01, 6.21], but not of being small for gestational age with a postnatal morbidity. Full vegetarians had marginally increased the odds of inadequate second-trimester gestational weight gain (ORadj = 2.24, 95% confidence interval: 0.95, 5.27).

Conclusion

Vegetarian diets during pregnancy were associated with constitutionally smaller neonatal size, potentially via the mothers’ reduced gestational weight gain. Notably, vegetarianism was not associated with small-for-gestational-age-related morbidities or other adverse maternal outcomes.

Keywords: Vegetarianism, pregnancy, neonatal size, maternal outcomes

Key Messages

  • In a diverse sample of US pregnant women, vegetarian diets were relatively common, with 6% of women self-defining as vegetarian and 2% meeting the criteria as full vegetarian based on their reported dietary intake.

  • A vegetarian diet during pregnancy, measured by food-frequency-questionnaire intake but not self-definition, was associated with a 2.5-fold increased risk of delivering a small-for-gestational-age neonate.

  • However, a vegetarian diet was not associated with having a small-for-gestational-age neonate with postnatal morbidity, suggesting that neonates of vegetarian mothers are constitutionally smaller.

  • A vegetarian diet during pregnancy was not associated with gestational diabetes, hypertensive disorders of pregnancy or gestational anaemia.

  • These findings provide important evidence that can help to inform dietary guidelines for pregnant women, although they are based on a limited sample size of vegetarians and require replication.

Introduction

Diets low in animal-based foods are gaining global attention as being beneficial to human and planetary health.1 The 2015 US Dietary Guidelines for Americans listed a ‘healthy vegetarian’ diet as one of three recommended dietary patterns.2 In the general population, vegetarian diets have been associated with a decreased risk of overweight,3,4 diabetes5 and coronary diseases.6 Though estimates vary widely, the prevalence of vegetarianism in the USA had been reported to be as high as 5% as of 2012 and is higher among women than men (7% vs 4%).7

Given its substantial prevalence among women, it is important to understand the possible health effects of vegetarianism during pregnancy—a sensitive stage of the lifecycle in which dietary choices can have meaningful implications. In 2009, the Academy of Nutrition and Dietetics stated that ‘vegetarian diets can be nutritionally adequate in pregnancy and result in positive maternal and infant health outcomes’.8 This endorsement was supported by limited evidence.9,10 For example, one of the conclusions in the position statement—that birth outcomes do not differ between vegetarian and non-vegetarian pregnant women—was reached from a review of only four primary studies.11–15 Some of these studies exhibited methodological shortcomings, such as a lack of an appropriate comparison group, and none was conducted in a US population.9 Another consideration is the lack of standardized criteria for defining vegetarian diets, which complicates matters, since certain individuals self-identify as vegetarians but do not highly restrict, let alone strictly avoid, the intake of meat, poultry and/or fish.16–18

Our objective was to comprehensively assess associations between vegetarian diets during pregnancy with neonatal and maternal outcomes, using self-identified vegetarianism in combination with a diet-based definition, among a contemporary, prospective, diverse cohort of US pregnant women.

Methods

Study population

The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies–Singletons was a prospective cohort of women with singleton pregnancies designed primarily to establish standards for fetal growth.19 Approximately equal numbers of self-identified non-Hispanic White, non-Hispanic Black, Hispanic and Asian/Pacific Islander women were enrolled at 12 clinical sites around the USA from 8 to 13 weeks of gestation. Study participants were followed for up to five additional visits throughout pregnancy. The cohort included 2802 women, of whom 2334 were non-obese and 468 were obese. Of these, 1948 women were invited to the nutrition component of the study (which was deployed midway through recruitment) and had a live birth. Pre-existing chronic diseases (including asthma, autoimmune disorders, cancer, diabetes, thyroid disease, epilepsy and chronic hypertension) and lifestyle risk factors (including smoking, illicit drug use and daily alcohol intake) were exclusion criteria for non-obese women. The study was approved by the institutional review boards of the NICHD and all clinical and data coordinating centres (ClinicalTrials.gov, NCT00912132). All women provided written informed consent prior to enrolment. Details of the cohort were described elsewhere.20

Assessment of vegetarianism during pregnancy

Self-defined vegetarianism was defined using participants’ yes/no responses to the question: ‘For ALL of the past 3 months, have you followed a vegetarian diet?’ Diet-based vegetarianism was determined from the frequency category for each meat-, poultry- and fish-based food item on a food-frequency questionnaire (FFQ) administered at enrolment reflecting intake over the past 3 months. The FFQ was a modified version of the Diet History Questionnaire-2. Consistently with previous literature,21 we defined ‘full vegetarians’ as women who never ate meat, poultry and fish, or ate these foods less than once a month; ‘pesco-vegetarians’ as women who ate meat and poultry less than once a month but had no restriction on fish; and ‘semi-vegetarians’ as women who ate meat, poultry and fish greater than once a month, but less than once a week. The full-vegetarian group included vegans (who also avoid eggs and dairy products); we did not further stratify this group in the analysis due to the small sample size. Implausible dietary intakes (<600 or >6000 kcal/day) were set to missing and imputed for all analyses (n = 74).

As women may change their diets throughout pregnancy, we further defined ‘sustained vegetarianism’ as a participant who reported being a diet-based full vegetarian via FFQ at baseline and also reported no intake of meat, poultry or fish in at least three out of four 24-hour recalls during pregnancy. Automated self-administered 24-hour recalls (ASA-24) were taken at 16–22, 24–29, 30–33 and 34–37 weeks of gestation and have demonstrated validity.22,23

Neonatal outcomes

Neonatal outcomes included measures of anthropometry (birthweight, birth length, upper-arm length, upper-thigh length, head circumference, abdominal circumference, sum of skinfold thickness), small for gestational age (SGA), large for gestational age (LGA), low birthweight (LBW) (<2500 g), macrosomia (≥4000 g), preterm birth (<37 weeks) and neonatal morbidity. Birthweight was abstracted from medical charts after delivery and other anthropometrics were measured by trained research nurses using standardized protocols.24–28 Gestational age was calculated from the self-reported last-menstrual-period date confirmed through first-trimester ultrasound. SGA and LGA were categorized using sex-specific definitions from the US reference by Duryea et al.29 To distinguish pathologically small and large neonates from those constitutionally sized,30 we classified SGA and LGA with neonatal morbidities. Neonatal morbidities, which were abstracted from medical records, included: metabolic acidosis (pH <7.1 and base deficit >12 mmol/L), neonatal intensive-care-unit stay >3 days, pneumonia, respiratory distress syndrome, persistent pulmonary hypertension, seizures, hyperbilirubinemia requiring exchange transfusion, intrapartum aspiration (meconium, amniotic fluid, blood), neonatal death, mechanical ventilation at term, necrotizing enterocolitis, hypoglycaemia, hypoxic ischaemic encephalopathy, periventricular leukomalacia (SGA only), sepsis based on blood culture (SGA only), bronchopulmonary dysplasia/chronic lung disease (SGA only), retinopathy of prematurity (SGA only) and birth injury (LGA only).31–36

Maternal outcomes

Maternal outcomes included measures of gestational weight gain, gestational diabetes, hypertensive disorders of pregnancy and anaemia. Each woman reported her pre-pregnancy weight at enrolment. At each follow-up visit, weight was measured using standardized protocols,24,37 as well as abstracted from prenatal-care-clinic charts. Total weight gain was estimated up to the date of delivery, along with weight gain in each trimester, and categorized as per Institute of Medicine recommendations (inadequate, adequate and excessive).38 Glycaemic status was categorized as: gestational diabetes (defined using a combination of oral-glucose-tolerance-test results based on Carpenter and Coustan criteria, and medication treatment abstracted from medical records),39,40 impaired blood glucose (2-hour post-load plasma glucose 7.8–11.0 mmol/l) and normoglycaemia. The presence and severity of pre-eclampsia/hypertension was determined by a physician based on the standard of care at each study clinic. Women were categorized as: no hypertension; mild gestational hypertension and unspecified hypertension; or severe gestational hypertension and severe/mild pre-eclampsia.41,42 The presence of gestational anaemia was abstracted from prenatal-care records.

Covariate data

At enrolment, research nurses interviewed women to obtain socio-demographic characteristics and reproductive history. Women self-completed a validated physical-activity questionnaire.43 Pre-pregnancy body mass index (BMI) was calculated from self-reported weight and measured height. Infant sex was determined at delivery. Dietary covariates included total energy intake and diet quality using a modified version of the Healthy Eating Index-2010 (HEI-2010).44 ‘Total protein foods’ and ‘seafood and plant proteins’ were excluded from the HEI-2010 because vegetarian groups would directly and systemically affect these two components.

Statistical analysis

Descriptive characteristics of participants, differentiated by vegetarian status (self-defined and diet-based), were compared using chi-squared, t-tests and analysis of variance (ANOVA), as appropriate. Since our study oversampled racial/ethnic minorities, we estimated the prevalence of vegetarian-status weighting according to the racial/ethnic distributions of US women with low-risk singleton pregnancies from 2011 Vital Statistics.45 Linear regression was used to estimate associations of vegetarian status with continuous neonatal anthropometric measurements. Adjusted risk ratios from log-binomial models and odds ratios (ORadj) from logistic regression were estimated for binary and polytomous outcomes, respectively. Non-vegetarians were the reference group for all models. Fully adjusted models accounted for maternal age, height, pre-pregnancy BMI, parity, race-ethnicity, marital status, education, income, current job/student status, insurance coverage, study site, infant sex, total weekly physical activity, total energy intake and diet quality. All models of birth length, upper-arm length, upper-thigh length, head circumference, abdominal circumference and skinfold thickness were also adjusted for the time between postnatal measurement and the delivery date. Models of neonatal outcomes were not adjusted for gestational age because this factor may be in the causal pathway and adjustment may induce bias.46 Missing exposure, covariate and outcome data were multiply imputed (20 iterations).47 As a sensitivity analysis, for all outcomes that were associated with diet-based vegetarianism, we further evaluated the associations based on whether vegetarianism was sustained through pregnancy. All analyses were performed using SAS 9.4 (SAS Institute, Cary, NC, USA).

Results

The weighted prevalence of self-defined vegetarianism was 6.2%. Using diet-based definitions, the weighted prevalence of full, pesco- and semi-vegetarianism was 2.0%, 0.6% and 17.6%, respectively. Of the 99 self-defined vegetarians, only 22 were found to be diet-based full vegetarians.

Compared with their non-vegetarian counterparts, self-defined and diet-based full vegetarians were more highly educated, had higher incomes and were more likely to have private health insurance (Table 1). Self-defined and diet-based full vegetarians were also more likely to be Asian/Pacific Islanders. Although self-defined vegetarians had lower mean pre-pregnancy BMI than non-vegetarians (24.2 vs 25.4 kg/m2, p = 0.02), there was no appreciable difference in the mean reported daily total energy or macronutrient intakes between the two groups. The modified HEI-2010, however, was higher in self-defined vegetarians (61.2 vs 56.1, p < 0.01), indicating better diet quality. The mean pre-pregnancy BMI in diet-based full vegetarians (23.4 kg/m2) was appreciably lower than that in non-vegetarians (25.4 kg/m2) (pair-wise p = 0.04). The mean total energy intake varied between the groups: 1678 kcal/day among full vegetarians, 2020 kcal/day among pesco-vegetarians, 1649 kcal/day among semi-vegetarians and 2304 kcal/day among non-vegetarians (p < 0.01). Macronutrient intake also varied across groups, with the mean modified HEI-2010 being highest among pesco-vegetarians (66.0) and lowest among non-vegetarians (56.5) (p < 0.01).

Table 1.

Description of cohort by self-defined and diet-based vegetarian status, the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies–Singletons 2009–2013

Self-defined (n = 1633)
 Diet-based (n = 1596)
Mean ± SD or N (%)
 Mean ± SD or N (%)
Non-vegetarian (n = 1534) Vegetarian (n = 99) P-value Non-vegetarian (n = 1256) Vegetarian (n = 32) Pesco- vegetarian (n = 7) Semi- vegetarian (n = 301) P-value
Age, year 27.9 ± 5.6 29.9 ± 5.5 0.0006 28.1 ± 5.5 29.6 ± 5.1 32.1 ± 4.7 27.7 ± 6.1 0.05
Height, cm 162.4 ± 6.9 163.1 ± 6.2 0.32 162.5 ± 7.1 161.7 ± 5.6 161.9 ± 5.3 162.1 ± 6.2 0.77
BMI, kg/m2 25.4 ± 5.2 24.2 ± 4.2 0.02 25.4 ± 5.1 23.4 ± 4.2 24.2 ± 4.6 25.4 ± 5.1 0.18
Gestational age, weeks 39.2 ± 1.9 39.1 ± 2.2 0.79 39.1 ± 2.0 38.8 ± 3.2 39.9 ± 1.3 39.3 ± 1.3 0.18
Race/ethnicity
 Non-Hispanic White 312 (20.34) 22 (22.22) 271 (21.58) 7 (21.88) 3 (42.86) 51 (16.94)
 Non-Hispanic Black 485 (31.62) 21 (21.21) 386 (30.73) 3 (9.38) 2 (28.57) 84 (27.91)
 Hispanic 460 (29.99) 26 (26.26) 365 (29.06) 9 (28.13) 0 (0) 112 (37.21)
 Asian/Pacific Islander 277 (18.06) 30 (30.30) 0.01 234 (18.63) 13 (40.63) 2 (28.57) 54 (17.94) <0.01
Education
 <High school 171 (11.15) 13 (13.13) 137 (10.91) 0 (0) 0 (0) 45 (14.95)
 High school/GED 314 (20.47) 13 (13.13) 240 (19.11) 1 (3.13) 1 (14.29) 70 (23.26)
 Some college/associates 489 (31.88) 24 (24.24) 384 (30.57) 10(31.25) 1 (14.29) 103 (34.22)
 Undergraduate degree 326 (21.25) 21 (21.21) 290 (23.09) 8 (25.00) 4 (57.14) 44 (14.62)
 Postgraduate degree 234 (15.25) 28 (28.28) 0.01 205 (16.32) 13(40.63) 1 (14.29) 39 (12.96) <0.01
Household income
 <30 000 449 (34.57) 21 (25.61) 361 (33.77) 4 (14.29) 0 (0) 78 (32.64)
 $30 000–$39 999 117 (9.01) 7 (8.54) 93 (8.70) 3 (10.71) 0 (0) 24 (10.04)
 $40 000–$49 999 109 (8.39) 4 (4.88) 79 (7.39) 0 (0) 1 (14.29) 32 (13.39)
 $50 000–$74 999 160 (12.32) 12 (14.63) 130 (12.16) 10 (35.71) 0 (0) 31 (12.97)
 $75 000–$99 999 171 (13.16) 5 (6.10) 148 (13.84) 1 (3.57) 1 (14.29) 23 (9.62)
 ≥$100 000 293 (22.56) 33 (40.24) 0.01 258 (24.13) 10 (35.71) 5 (71.43) 51 (21.34) <0.01
Current full-time job or school
 Yes 1052 (68.58) 74 (74.75) 872 (69.43) 26 (81.25) 7 (100) 196 (65.12)
 No 482 (31.42) 25 (25.25) 0.20 384 (30.57) 6 (18.75) 0 (0) 105 (34.88) 0.05
Insurance
 Private/managed care 868 (58.26) 65 (69.89) 730 (60.03) 23 (74.19) 7 (100) 162 (55.29)
 Other 622 (41.74) 28 (30.11) 0.03 486 (39.97) 8 (25.81) 0 (0) 131 (44.71) 0.02
Marital status
 Not married 433 (28.25) 22 (22.22) 328 (26.11) 6 (18.75) 3 (42.86) 88 (29.33)
 Married or living with partner 1100 (71.75) 77 (77.78) 0.20 928 (73.89) 26 (81.25) 4 (57.14) 212 (70.67) 0.35
Parity
 0 699 (45.57%) 52 (52.53) 593 (47.21) 15 (46.88) 5 (71.43) 122 (40.53)
 1 529 (34.40%) 31 (31.31) 410 (32.64) 15 (46.88) 2 (28.57) 122 (40.53)
 2 529 (34.40%) 9 (9.09) 167 (13.30) 1 (3.13) 0 (0) 42 (13.95)
 3 75 (4.89%) 4 (4.04) 67 (5.33) 0 (0) 0 (0) 10 (3.32)
 4 and up 23 (1.50) 3 (3.03) 0.39 19 (1.51) 1 (3.13) 0 (0) 5 (1.66) 0.13
Infant sex
 Male 747 (50.47) 42 (45.65) 612 (50.62) 13 (41.94) 4 (57.14) 148 (51.03)
 Female 733 (49.53) 50 (54.35) 0.37 597 (49.38) 18 (58.06) 3 (42.86) 142 (48.97) 0.78
Total calories, kcal/day 2166.0 ± 1029.8 2123.9 ± 946.1 0.70 2304.3 ± 1038.2 1678.2 ± 742.8 2020.2 ± 860.2 1649.1 ± 867.7 <0.0001
Carbohydrate, gm/day 291.3 ± 161.7 293.6 ± 144.2 0.89 305.2 ± 162.7 234.6 ± 106.9 275.5 ± 107.7 246.6 5 ± 158.8 <0.0001
Protein, gm/day 84.1 ± 40.9 81.6 ± 37.1 0.57 91.3 ± 40.5 56.2 ± 27.2 83.8 ± 31.3 56.1 ± 29.3 <0.0001
Fat, gm/day 78.7 ± 40.3 76.1 ± 36.2 0.54 84.8 ± 40.5 63.3 ± 34.3 72 ± 40.7 53.5 ± 28.7 <0.0001
HEI-2010 score 56.4 ± 9.5 61.1 ± 10.1 <0.0001 56.5 ± 9.5 61.9 ± 10.9 66.0 ± 8.5 56.3 ± 9.4 0.0007
Takes prenatal or multivitamins
 Yes 1318 (88.58) 87 (93.55) 1083 (89.21) 30 (96.77) 6 (85.71) 262 (89.42) 0.59
 No 170 (11.42) 6 (6.45) 0.14 131 (10.79) 1 (3.23) 1 (14.29) 31 (10.58)
Had severe vomiting/hyperemesis
 Yes 77 (5.02) 8 (8.08) 57 (4.54) 5 (15.63) 0 (0) 20 (6.64) 0.02
 No 1457 (94.98) 91 (91.92) 0.18 1199 (95.46) 27 (84.38) 7 (100) 281 (93.36) 0.01
Highest systolic blood pressure 123.8 (13.5) 123.3 (12.9) 0.83 123.8 (13.6) 117.9 (13.9) 139.0 (9.9) 123.8 (12.9) 0.15
Highest diastolic blood pressure 75.1 (10.1) 76.2 (9.6) 0.52 75.1 (10.0) 70.6 (8.4) 87.0 (1.4) 75.2 (10.1) 0.13
Total physical activity, MET hours/week 323.1 ± 165.3 323.3 ± 178.2 0.99 326.0 ± 163.0 319.3 ± 157.5 374.0 ± 205.1 292.5 ± 148.8
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BMI, body mass index (calculated as weight in kilograms divided by height in metres squared); HEI-2010, Healthy Eating Index-2010 (without total protein foods and seafood /plant proteins components); MET, metabolic equivalent of task.

P-values were derived using two-sample t-tests for self-defined vegetarianism and analysis of variance (ANOVA) for diet-based vegetarianism.

Missing data: For both self-defined and diet-based vegetarianism, n = 11 for height; n = 25 for income; n = 1 for marital status; n = 67 for calories, carbohydrate, protein and fat; n = 2 for physical activity. For self-defined vegetarianism, n = 62 for gestational age, n = 2 for current job/school, n = 50 for insurance, n = 61 for infant sex, n = 52 for prenatal or multivitamins and n = 779 for highest systolic and diastolic blood pressure. For diet-based vegetarianism, n = 60 for gestational age, n = 3 for current job/school, n = 49 for insurance, n = 59 for infant sex, n = 51 for prenatal or multivitamins and n = 944 for highest systolic and diastolic blood pressure. Numbers with missing data for calories, carbohydrate, protein and fat (n = 67) include those with implausible values.

Highest systolic and diastolic blood pressure were abstracted from a maximum of eight prenatal-care records. Total physical activity reflects weekly activity in the past year.

Mean birthweight and length were lower among neonates of self-defined [birthweightβadj = –117.11, 95% confidence (CI): –235.53, 1.33; length βadj = –0.58, 95% CI: –1.17, 0.01] and diet-based full vegetarians (birthweightβadj = –202.02, 95% CI: –383.49, –20.56; length βadj = –1.01, 95% CI: –1.93, –0.09) (Table 2). Diet-based full vegetarians also had neonates with lower upper-thigh length (βadj = –0.53, 95% CI: –0.96, –0.11) and had higher odds of delivering neonates that were SGA (ORadj = 2.51, 95% CI: 1.01, 6.21) or LBW (ORadj = 3.86, 95% CI: 1.30, 11.45) than their non-vegetarian counterparts. Semi-vegetarians also had higher odds of delivering SGA neonates (ORadj = 1.98, 95% CI: 1.24, 3.17). Only 1% of neonates in the overall sample had both SGA and morbidity, leading to a very imprecise association of this outcome with vegetarianism.

Table 2.

Associations of vegetarianism with neonatal outcomes, the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies–Singletons, 2009–2013

Overall mean (SD) or proportiona Self-defined vegetarianism
 Diet-based vegetarianism
Unadjusted
β (95% CI)		 Adjusted
β (95% CI)		 Unadjusted
β (95% CI)		 Adjusted
β (95% CI)
Birthweight (grams) 3314.3 (535.7) Vegetarian –92.38 (–213.43, 28.66) –117.11 (–235.53, 1.33) Full vegetarian –202.08 (–385.51, –18.64) –202.02 (–383.49, –20.56)
Pesco-vegetarian 10.20 (–376.08, 396.48) –56.26 (–428.29, 315.76)
Semi-vegetarian 12.38 (–58.09, 82.84) 3.12 (–67.42, 73.66)
Birth length (cm) b 49.96 (2.67) Vegetarian –0.41 (–1.00, 0.17) –0.58 (–1.17, 0.01) Full vegetarian –0.88 (–1.82, 0.06) –1.01 (–1.93, –0.09)
Pesco-vegetarian –0.65 (–2.57, 1.28) –0.80 (–2.69, 1.09)
Semi-vegetarian 0.03 (–0.33, 0.39) 0.08 (–0.28, 0.45)
Upper-arm length (cm) b 10.10 (1.13) Vegetarian –0.02 (–0.28, 0.23) –0.14 (–0.38, 0.11) Full vegetarian –0.17 (–0.53, 0.19) –0.25 (–0.60, 0.79)
Pesco-vegetarian 0.35 (–0.47, 1.16) 0.01 (–0.76, 0.79)
Semi-vegetarian –0.04 (–0.18, 0.10) –0.001 (–0.14, 0.13)
Upper-thigh length (cm) b 10.44 (1.40) Vegetarian –0.05 (–0.36, 0.25) –0.14 (–0.43, 0.16) Full vegetarian –0.52 (–0.96, –0.09) –0.53 (–0.96, –0.11)
Pesco-vegetarian –0.56 (–1.58, 0.46) –0.83 (–0.18, 0.12)
Semi-vegetarian –0.05 (–0.24, 0.13) –0.02 (–0.21, 0.17)
Head circumference (cm) b 31.20 (2.76) Vegetarian 0.004 (–0.37, 0.37) –0.09 (–0.45, 0.27) Full vegetarian –0.26 (–0.81, 0.29) –0.33 (–0.86, 0.21)
Pesco-vegetarian 0.17 (–1.02, 1.36) –0.12 (–1.28, 1.03)
Semi-vegetarian 0.10 (–0.11, 0.32) 0.07 (–0.15, 0.28)
Abdominal circumference (cm) b 33.96 (1.68) Vegetarian –0.36 (–1.02, 0.30) –0.47 (–1.11, 0.17) Full vegetarian –0.72 (–1.75, 0.31) –0.73 (–1.73, 0.27)
Pesco-vegetarian 0.07 (–1.96, 2.11) –0.04 (–1.95, 1.86)
Semi-vegetarian 0.03 (–0.34, 0.39) –0.04 (–0.41, 0.33)
Sum of skinfold thickness (mm) b 20.31 (5.12) Vegetarian –0.52 (–1.63, 0.60) –0.44 (–1.51, 0.62) Full vegetarian –1.74 (–3.48, –0.001) –1.44 (–3.14, 0.27)
Pesco-vegetarian 1.87 (–2.07, 5.81) 0.88 (–2.75, 4.51)
Semi-vegetarian –0.09 (–0.75, 0.56) –0.25 (–0.95, 0.45)

Unadjusted

OR (95% CI)

Adjusted

OR (95% CI)

Unadjusted

OR (95% CI)

Adjusted

OR (95% CI)
Size for gestational age
Small for gestational age (SGA) 9.17% Vegetarian 0.86 (0.40, 1.85) 0.92 (0.42, 2.04) Full vegetarian 2.17 (0.93, 5.06) 2.51 (1.01, 6.21)
Pesco-vegetarian — —
Semi-vegetarian 1.66 (1.09, 2.52) 1.98 (1.24, 3.17)
Large for gestational age (LGA) 8.14% Vegetarian 0.93 (0.43, 1.98) 0.81 (0.36, 1.83) Full vegetarian 0.70 (0.17, 2.93) 0.69 (0.16, 3.07)
Pesco-vegetarian — —
Semi-vegetarian 1.15 (0.75, 1.77) 1.23 (0.77, 1.99)
Neonatal size and morbidity
SGA with morbidity 1.03% Vegetarian 0.88 (0.00, 3.58) 1.35 (0.00, –) Full vegetarian 5.17 (0.87, 30.68) 9.20 (0.83, 101.91)
Pesco-vegetarian — —
Semi-vegetarian 0.58 (0.08, 4.41) 0.57 (0.05, 6.13)
SGA without morbidity 8.15% Vegetarian 0.75 (0.33, 1.71) 0.79 (0.34, 1.82) Full vegetarian 1.69 (0.64, 4.47) 1.94 (0.70, 5.35)
Pesco-vegetarian — —
Semi-vegetarian 1.80 (1.17, 2.77) 2.14 (1.32, 3.45)
LGA with morbidity 0.83% Vegetarian — — Full vegetarian — —
Pesco-vegetarian — —
Semi-vegetarian 1.69 (0.54, 5.29) 1.70 (0.45, 6.42)
LGA without morbidity 7.30% Vegetarian 1.03 (0.48, 2.20) 0.88 (0.39, 1.99) Full vegetarian 0.76 (0.18, 3.28) 0.72 (0.16, 3.29)
Pesco-vegetarian — —
Semi-vegetarian 1.10 (0.69, 1.74) 1.18 (0.70, 1.96)
Birthweight category
Low birthweight 5.40% Vegetarian 1.40 (0.60, 3.28) 1.73 (0.69, 4.33) Full vegetarian 2.70 (1.01, 7.24) 3.86 (1.30, 11.45)
Pesco-vegetarian — —
Semi-vegetarian 1.11 (0.61, 1.99) 1.38 (0.73, 2.61)
Macrosomia 8.14% Vegetarian 0.64 (0.24, 1.75) 0.60 (0.22, 1.69) Full vegetarian 0.001 (0.00, –) 0.01 (0.00, – )
Pesco-vegetarian — —
Semi-vegetarian 1.02 (0.64, 1.62) 1.03 (0.62, 1.71)
Preterm birth (<37 weeks) 6.12% Vegetarian 1.39 (0.62, 3.13) 1.63 (0.66, 4.02) Full vegetarian 1.71 (0.61, 4.83) 1.94 (0.60, 6.29)
Pesco-vegetarian — —
Semi-vegetarian 0.61 (0.32, 1.18) 0.65 (0.32, 1.30)
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OR, odds ratio from logistic regression; SD, standard deviation; SGA, small for gestational age; LGA, large for gestational age.

Adjusted models control for age, height, parity, pre-pregnancy BMI, race, marital status, education, income, current job/student status, insurance coverage, infant sex, total weekly physical activity, total energy and Healthy Eating Index-2010 (without total protein foods and seafood/plant-protein components). Non-estimable 95% CIs presented as –. Non-estimable OR 95% CIs presented as —.

Multiple imputation (20 iterations) used to address missing exposure, outcome and covariate data.

a

Mean or proportion in 20 imputed data sets (n = 38 960).

b

Also adjusted for measurement date.

Diet-based full vegetarians had marginally increased odds of inadequate gestational weight gain during the second trimester (ORadj = 2.24, 95% CI: 0.95, 5.27) (Table 3). Vegetarianism did not exhibit associations with any other maternal outcomes, including gestational diabetes, hypertensive disorders and anaemia.

Table 3.

Associations of vegetarianism with maternal outcomes, the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies–Singletons, 2009–2013

Overall mean (SD) or proportiona Self-defined vegetarianism
 Diet-based vegetarianism
Unadjusted
OR (95% CI)		 Adjusted
OR (95% CI)		 Unadjusted
OR (95% CI)		 Adjusted
OR (95% CI)
Total GWG by IOM criteria
 Inadequate GWG 33.79% Vegetarian 0.97 (0.58, 1.62) 1.04 (0.61, 1.76) Full vegetarian 1.23 (0.59, 2.59) 1.25 (0.57, 2.74)
Pesco-vegetarian 0.82 (0.12, 5.76) 1.38 (0.18, 10.67)
Semi-vegetarian 0.95 (0.68, 1.33) 0.88 (0.60, 1.28)
 Excessive GWG 36.13% Vegetarian 0.92 (0.55, 1.56) 1.00 (0.57, 1.72) Full vegetarian 0.63 (0.26, 1.57) 0.78 (0.30, 2.01)
Pesco-vegetarian 1.25 (0.21, 7.40) 1.33 (0.21, 8.54)
Semi-vegetarian 1.10 (0.81, 1.49) 1.12 (0.80, 1.58)
Second-trimester GWG by IOM
 Inadequate GWG 47.39% Vegetarian 1.12 (0.68, 1.84) 1.28 (0.76, 2.16) Full vegetarian 2.07 (0.92, 4.69) 2.24 (0.95, 5.27)
Pesco-vegetarian 1.88 (0.20, 18.09) 2.88 (0.29, 28.54)
Semi-vegetarian 1.17 (0.87, 1.57) 1.05 (0.76, 1.44)
 Excessive GWG 25.26% Vegetarian 1.12 (0.63, 2.01) 1.42 (0.77, 2.63) Full vegetarian 1.19 (0.41, 3.55) 1.68 (0.53, 5.29)
Pesco-vegetarian 3.56 (0.38, 33.31) 4.97 (0.49, 50.91)
Semi-vegetarian 1.29 (0.91, 1.84) 1.24 (0.83, 1.85)
Third-trimester GWG by IOM
 Inadequate GWG 26.68% Vegetarian 0.98 (0.57, 1.68) 1.13 (0.64, 1.99) Full vegetarian 1.69 (0.79, 3.61) 2.03 (0.89, 4.65)
Pesco-vegetarian — —
Semi-vegetarian 1.21 (0.87, 1.68) 1.08 (0.74, 1.57)
 Excessive GWG 35.93% Vegetarian 1.00 (0.61, 1.64) 1.19 (0.70, 2.03) Full vegetarian 0.73 (0.30, 1.79) 1.01 (0.38, 2.66)
Pesco-vegetarian 0.80 (0.18, 3.56) 0.81 (0.16, 4.16)
Semi-vegetarian 1.22 (0.89, 1.67) 1.20 (0.84, 1.71)
Glycaemic status
 Impaired glucose tolerance 4.16% Vegetarian 0.85 (0.30, 2.41) 0.83 (0.27, 2.51) Full vegetarian 1.32 (0.40, 4.43) 1.08 (0.28, 4.12)
Pesco-vegetarian — —
Semi-vegetarian 0.80 (0.43, 1.51) 0.97 (0.48, 1.93)
 Gestational diabetes 4.36% Vegetarian 1.25 (0.52, 3.05) 1.16 (0.43, 3.07) Full vegetarian 0.83 (0.15, 4.71) 0.88 (0.15, 5.17)
Pesco-vegetarian — —
Semi-vegetarian 0.76 (0.40, 1.45) 0.93 (0.46, 1.89)
Hypertensive disorders
 Mild gestational/ unspecified hypertension 2.98 % Vegetarian 0.84 (0.26, 2.75) 1.25 (0.35, 4.38) Full vegetarian 0.68 (0.09, 5.06) 1.48 (0.18, 12.21)
Pesco-vegetarian — —
Semi-vegetarian 1.43 (0.76, 2.69) 1.57 (0.77, 3.20)
 Severe gestational 3.23% Vegetarian 0.60 (0.14, 2.50) 0.65 (0.15, 2.91) Full vegetarian 0.60 (0.08, 4.51) 0.83 (0.10, 6.90)
Hypertension/pre-eclampsia Pesco-vegetarian — —
Semi-vegetarian 0.48 (0.18, 1.25) 0.54 (0.20, 1.44)

Unadjusted

RR (95% CI)

Adjusted

RR (95% CI)

Unadjusted

RR (95% CI)

Adjusted

RR (95% CI)
Gestational anaemia 24.38% Vegetarian 0.79 (0.54, 1.16) 0.96 (0.66, 1.41) Full vegetarian 0.64 (0.33, 1.23) 0.73 (0.38, 1.39)
Pesco-vegetarian 1.09 (0.32, 3.66) 1.65 (0.49, 5.52)
Semi-vegetarian 1.03 (0.82, 1.29) 1.01 (0.80, 1.28)
Open in a new tab

OR, odds ratio from logistic regression; RR, relative risk from log-binomial regression; SD, standard deviation; GWG, gestational weight gain; IOM, Institute of Medicine.

Adjusted models control for age, height, parity, pre-pregnancy BMI, race, marital status, education, income, current job/student status, insurance coverage, infant sex, total weekly physical activity, total energy and Healthy Eating Index-2010 (without total protein foods and seafood/plant-protein components). Non-estimable OR (95% CI)s presented as —.

Multiple imputation (20 iterations) used to address missing exposure, outcome and covariate data.

a

Mean or proportion in 20 imputed data sets (n = 38 960).

In a sensitivity analysis using data from ASA-24 recalls later in pregnancy, we found that 7 of the 32 (21.9%) diet-based full vegetarians were sustained vegetarians. Sustained vegetarianism exhibited an imprecise association with SGA (ORadj = 9.97, 95% CI: 1.86, 53.59); the association with LBW was ORadj = 4.22, 95% CI: 0.37, 47.44.

Discussion

In this diverse sample of US pregnant women, vegetarian diets were relatively common, with 6% of women self-defining as vegetarian and 2% meeting criteria as full vegetarian based on reported dietary intake. Diet-based full vegetarianism was associated with lower birthweight and increased odds of SGA, potentially linked to reductions in gestational weight gain. Importantly, no associations were observed between vegetarianism and SGA with neonatal morbidities, suggesting that the growth restriction is likely constitutional, though the number of infants with morbidities was limited. These associations with neonatal outcomes were not as evident with self-defined vegetarianism. Also, no protective associations were observed between vegetarianism and adverse maternal outcomes, indicating the lack of maternal-health benefits. These results provide important evidence regarding the impact of vegetarian diets during pregnancy on both neonatal and maternal health.

Previous research on the topic has been limited and yielded inconsistent findings. For example, in a 2015 review, Piccoli et al.10 reported that five studies found lower birthweight in neonates of vegetarian mothers, whereas two studies found higher birthweight. The birthweight differences observed in these studies ranged from 20 to 200 grams,10 which is similar in magnitude to our findings. The clinical interpretation of prior findings is uncertain, since one cannot determine whether the lower mean observed birthweight was due to a reduction in the number of LGA babies, an increase in the number of SGA babies or a shift towards lower weights that still fall within the normal range.9

Our study stands out in that we found associations of maternal vegetarian diets with SGA—a clinically meaningful outcome that can indicate in utero undernutrition and has been associated with adverse outcomes even later in life.48 On balance, however, our findings do not suggest that following a vegetarian diet during pregnancy is associated with pathologically smaller neonates. Specifically, we did not observe associations with SGA-related morbidity. As a caveat, the number of infants with these outcomes was small, limiting the power of the analysis to detect related associations. Moreover, most of the diet-based vegetarians in our sample were Asian and the suitability of the traditional SGA definition for Asians (who generally have smaller neonates) is an area of debate.49,50 For these reasons, our findings should be interpreted with caution.

The lower birthweight and increased odds of SGA that we observed are not likely explained by earlier delivery. No associations were found with preterm birth. Instead, inadequate second-trimester gestational weight gain among diet-based full vegetarians showed a marginal association and may play a role. One hypothesis is that vegetarian diets do not provide the necessary substrates—both macro- and micronutrients—to meet the physiological demands of a developing fetus. Protein is critical for the tissue expansion involved in fetal development. Without a careful assortment of plant foods to provide complementary proteins, vegetarians may have trouble meeting this dietary requirement.8 Another hypothesis is that the bioavailability of zinc in vegetarian diets can be low due to the high phytate content of unrefined grains and legumes.8 Zinc also plays an important role in fetal development and its deficiency has been associated with growth restriction.9,51 Consistently with these hypotheses, our data revealed that diet-based full vegetarians had substantially lower protein and zinc intake than non-vegetarians (56.2 vs 91.3 grams/day for protein; 9.4 vs 13.5 mg/day for zinc). The broader implication is that a more complete understanding of the key nutrients and biological processes involved in vegetarian diets among pregnant women is important for identifying points of intervention to lower the risk of the low birthweight of neonates. Lastly, although we accounted for a comprehensive set of covariates, residual confounding may be present.

Another noteworthy set of findings is the lack of protective associations between vegetarianism and adverse maternal outcomes. The cardiometabolic benefits of vegetarian diets have been documented in the general population,8,52 although our results suggest that these benefits may not apply during pregnancy. Another explanation could be that the associations are not strong enough to be observed in our low-risk sample of pregnant women and this diet may only be beneficial once women are at a certain level of increased cardiometabolic risk. A favourable finding is that the vegetarians in our study did not exhibit an increased risk of gestational anaemia—a leading cause of maternal morbidity that has previously been associated with vegetarian diets due to the lack of heme iron.53,54

Our study is the most comprehensive assessment of the associations of vegetarianism during pregnancy on maternal and neonatal outcomes in a US population. A strength of our study is the use of two definitions of vegetarianism (self-report and diet-based), which allowed a thorough assessment of dietary patterns. This approach was vital, since high discordance between self-defined vegetarian status and what individuals eat has been reported16–18 and was also observed in this study. Whereas self-defined vegetarianism appears to be an indicator of some level of animal-product avoidance and healthier diets, it results in overestimation of the prevalence of vegetarians as compared with diet-based definitions. In addition, we were able to assess the impact of sustaining vegetarian diets through pregnancy, whereas many previous studies only present diet data at one time point. Admittedly, there is no perfect way to match the diet-based definition of full vegetarianism from the FFQ with our 24-hour recall data and a single (not consecutive day) recall will tend to be an unrepresentative measure of typical intake. Future studies with more harmonious serial assessment of vegetarian status are needed to understand the trajectory of this dietary pattern. Furthermore, analyses that combine long-term vegetarianism status before pregnancy along with diet during pregnancy can add further insight into the health consequences of these diets. Our focus on pregnant women in the USA also represents an important contribution. The leading research conducted previously on this topic was based on Asian and European populations,12,13,15,55 which may not be fully applicable to US pregnant women due to cultural differences and food-market availability, which influence eating patterns, food composition and methods of food preparation. We rely on data from the NICHD Fetal Growth Study, which had extensive exclusion criteria (e.g. smoking and chronic diseases), leading to a sample of pregnant women who are mostly low-risk and with a lower prevalence of obesity. It remains to be seen whether our current findings hold in a sample that is more representative of US pregnant women. Another limitation is that the sample sizes of vegetarian groups (especially diet-based) were small and CIs for pesco-vegetarian outcomes were sometimes inestimable. However, the findings for SGA and LBW in a sample of only 32 full vegetarians also highlight the robustness of these associations.

In conclusion, our comprehensive analysis of maternal and neonatal outcomes in a contemporary sample of low-risk US pregnant women revealed an association of vegetarian diets with constitutionally smaller neonates, but no protective associations with adverse maternal outcomes. With replication in studies with larger sample sizes of vegetarians, our findings have the potential to inform nutrition counselling for pregnant women.

Funding

This work was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health, Bethesda, MD. Contracts: HHSN275200800013C, HHSN275200800002I, HHSN27500006, HHSN275200800003IC, HHSN275200800014C, HHSN275200800012C, HHSN275200800028C and HHSN275201000009C.

Acknowledgements

The clinical centres involved in data collection for the NICHD Fetal Growth Studies were (in alphabetical order): Christina Care Health Systems, Columbia University, Fountain Valley Hospital, California, Long Beach Memorial Medical Center, New York Hospital, Queens, Northwestern University, University of Alabama at Birmingham, University of California, Irvine, Medical University of South Carolina, Saint Peters University Hospital, Tufts University, and Women and Infants Hospital of Rhode Island. Clinical Trials & Surveys Corporation (C-TASC) and The Emmes Company were the data-coordinating centres that provided data and imaging support for this multi-site study. The protocol for the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Fetal Growth Studies–Singletons was approved by the Institutional Review Board of the National Institutes of Health on 5/27/2009 (#09-CH-N152). All participants provided written informed consent and confidentiality was maintained in accordance with the Declaration of Helsinki. The data and codebook, along with a set of guidelines for researchers applying for the data, will be posted in the future to a data-sharing site: the NICHD/DIPHR Biospecimen Repository Access and Data Sharing (https://brads.nichd.nih.gov) (BRADS). The analytic code for this manuscript is available upon request.

Conflict of interest

None declared.

References

  • 1. Willett W, Rockström J, Loken B. et al. Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. Lancet 2019;393:447–92. [DOI] [PubMed] [Google Scholar]
  • 2. Mozaffarian D, Ludwig DS.. The 2015 US dietary guidelines: lifting the ban on total dietary fat. JAMA 2015;313:2421–22. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3. Appleby PN, Thorogood M, Mann JI, Key TJ.. Low body mass index in non-meat eaters: the possible roles of animal fat, dietary fibre and alcohol. Int J Obes 1998;22:454–60. [DOI] [PubMed] [Google Scholar]
  • 4. Key T, Davey G.. Prevalence of obesity is low in people who do not eat meat. BMJ 1996;313:816–17. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5. Snowdon DA, Phillips RL.. Does a vegetarian diet reduce the occurrence of diabetes? Am J Public Health 1985;75:507–12. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6. Fraser GE, Lindsted KD, Beeson WL.. Effect of risk factor values on lifetime risk of and age at first coronary event: the Adventist Health Study. Am J Epidemiol 1995;142:746–58. [DOI] [PubMed] [Google Scholar]
  • 7. Newport F. In US, 5% Consider Themselves Vegetarians. Gallup Wellbeing, 2012. https://news.gallup.com/poll/156215/consider-themselves-vegetarians.aspx (11 September 2020, date last accessed). [Google Scholar]
  • 8. Craig WJ, Mangels AR.. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc 2009;109:1266–82. [DOI] [PubMed] [Google Scholar]
  • 9. Mariotti F. Vegetarian and Plant-Based Diets in Health and Disease Prevention. San Diego: Academic Press, 2017. [Google Scholar]
  • 10. Piccoli G, Clari R, Vigotti F. et al. Vegan–vegetarian diets in pregnancy: danger or panacea? A systematic narrative review. BJOG 2015;122:623–33. [DOI] [PubMed] [Google Scholar]
  • 11.American Dietetic Association. Vegetarian Nutrition in Pregnancy. American Dietetic Association Evidence Library. 2009. http://www.adaevidencelibrary.com (11 September 2020, date last accessed). [Google Scholar]
  • 12. Ganpule A, Yajnik C, Fall C. et al. Bone mass in Indian children—relationships to maternal nutritional status and diet during pregnancy: the Pune Maternal Nutrition Study. J Clin Endocrinol Metab 2006;91:2994–3001. [DOI] [PubMed] [Google Scholar]
  • 13. North K, Golding J, Team AS.. A maternal vegetarian diet in pregnancy is associated with hypospadias. BJU Int 2000;85:107–13. [DOI] [PubMed] [Google Scholar]
  • 14. Drake R, Reddy S, Davies J.. Nutrient intake during pregnancy and pregnancy outcome of lacto-ovo-vegetarians, fish-eaters and non-vegetarians. Veg Nutr 1998;2:45–52. [Google Scholar]
  • 15. Reddy S, Sanders T, Obeid O.. The influence of maternal vegetarian diet on essential fatty acid status of the newborn. Eur J Clin Nutr 1994;48:358–68. [PubMed] [Google Scholar]
  • 16. Barr SI, Chapman GE.. Perceptions and practices of self-defined current vegetarian, former vegetarian, and nonvegetarian women. J Am Diet Assoc 2002;102:354–60. [DOI] [PubMed] [Google Scholar]
  • 17. Finley DA, Dewey KG, Lonnerdal B, Grivetti LE.. Food choices of vegetarians and nonvegetarians during pregnancy and lactation. J Am Diet Assoc 1985;85:678–85. [PubMed] [Google Scholar]
  • 18. Haddad EH, Tanzman JS.. What do vegetarians in the United States eat? Am J Clin Nutr 2003;78:626s–32s. [DOI] [PubMed] [Google Scholar]
  • 19. Louis GMB, Grewal J, Albert PS. et al. Racial/ethnic standards for fetal growth: the NICHD Fetal Growth Studies. Am J Obstet Gynecol 2015;213:e1–41. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20. Grewal J, Grantz KL, Zhang C. et al. Cohort profile: NICHD fetal growth studies—singletons and twins. Int J Epidemiol 2018;47:25–l. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21. Jaacks LM, Kapoor D, Singh K. et al. Vegetarianism and cardiometabolic disease risk factors: differences between South Asian and US adults. Nutrition 2016;32:975–84. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22. Kirkpatrick SI, Subar AF, Douglass D. et al. Performance of the Automated Self-Administered 24-hour Recall relative to a measure of true intakes and to an interviewer-administered 24-h recall. Am J Clin Nutr 2014;100:233–40. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23. Subar AF, Kirkpatrick SI, Mittl B. et al. The Automated Self-Administered 24-hour dietary recall (ASA24): a resource for researchers, clinicians, and educators from the National Cancer Institute. J Acad Nutr Diet 2012;112:1134–37. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.National Health and Nutritional Examination Survey. Anthropometry Procedures Manual. 2007–2008. https://www.cdc.gov/nchs/data/nhanes/nhanes_07_08/manual_an.pdf (11 September2020, date last accessed).
  • 25. Catalano PM, Thomas AJ, Avallone DA, Amini SB.. Anthropometric estimation of neonatal body composition. Am J Obstet Gynecol 1995;173:1176–81. [DOI] [PubMed] [Google Scholar]
  • 26. Fok T, Hon K, Wong E. et al. Trunk anthropometry of Hong Kong Chinese infants. Early Hum Dev 2005;81:781–90. [DOI] [PubMed] [Google Scholar]
  • 27. Rodríguez G, Samper MP, Ventura P, Perez-Gonzalez JM.. Sex-specific charts for abdominal circumference in term and near-term Caucasian newborns. J Perinat Med 2008;36:527–30. [DOI] [PubMed] [Google Scholar]
  • 28. Stetzer BP, Thomas A, Amini SB, Catalano PM.. Neonatal anthropometric measurements to predict birth weight by ultrasound. J Perinatol 2002;22:397–402. [DOI] [PubMed] [Google Scholar]
  • 29. Duryea EL, Hawkins JS, McIntire DD, Casey BM, Leveno KJ.. A revised birth weight reference for the United States. Obstet Gynecol 2014;124:16–22. [DOI] [PubMed] [Google Scholar]
  • 30. Ananth CV, Vintzileos AM.. Distinguishing pathological from constitutional small for gestational age births in population-based studies. Early Hum Dev 2009;85:653–58. [DOI] [PubMed] [Google Scholar]
  • 31. Pugh SJ, Albert PS, Kim S. et al. Patterns of gestational weight gain and birthweight outcomes in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies-Singletons: a prospective study. Am J Obstet Gynecol 2017;217:346.e1–11. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32. Longo S, Bollani L, Decembrino L, Di Comite A, Angelini M, Stronati M.. Short-term and long-term sequelae in intrauterine growth retardation (IUGR). J Matern Fetal Neonatal Med 2013;26:222–25. [DOI] [PubMed] [Google Scholar]
  • 33. Rosenberg A. The IUGR newborn. Semin Perinatol 2008;32:219–24. [DOI] [PubMed] [Google Scholar]
  • 34. Giapros V, Drougia A, Krallis N, Theocharis P, Andronikou S.. Morbidity and mortality patterns in small-for-gestational age infants born preterm. J Matern Fetal Neonatal Med 2012;25:153–57. [DOI] [PubMed] [Google Scholar]
  • 35. McIntire DD, Bloom SL, Casey BM, Leveno KJ.. Birth weight in relation to morbidity and mortality among newborn infants. N Engl J Med 1999;340:1234–38. [DOI] [PubMed] [Google Scholar]
  • 36. King JR, Korst LM, Miller DA, Ouzounian JG.. Increased composite maternal and neonatal morbidity associated with ultrasonographically suspected fetal macrosomia. J Matern Fetal Neonatal Med 2012;25:1953–59. [DOI] [PubMed] [Google Scholar]
  • 37. Lohman TG, Roche AF, Martorell R.. Anthropometric Standardization Reference Manual. Champaign: Human Kinetics Books, 1988. [Google Scholar]
  • 38.National Research Council. Weight Gain during Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press, 2010. [PubMed] [Google Scholar]
  • 39.Committee on Practice Bulletins—Obstetrics. ACOG practice bulletin no. 190: gestational diabetes mellitus. Obstet Gynecol 2018;131:e49–64. [DOI] [PubMed] [Google Scholar]
  • 40. Zhu Y, Mendola P, Albert PS. et al. Insulin-like growth factor axis and gestational diabetes mellitus: a longitudinal study in a multiracial cohort. Diabetes 2016;65:3495–504. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.ACOG Committee on Obstetric Practice. ACOG practice bulletin No. 33: diagnosis and management of preeclampsia and eclampsia. American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet 2002;77:67–75. [PubMed] [Google Scholar]
  • 42. Mateus J, Newman RB, Zhang C. et al. Fetal growth patterns in pregnancy-associated hypertensive disorders: NICHD fetal growth studies. Am J Obstet Gynecol 2019;221:635.e1–16. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 43. Chasan-Taber L, Schmidt MD, Roberts DE, Hosmer D, Markenson G, Freedson PS.. Development and validation of a pregnancy physical activity questionnaire. Med Sci Sports Exerc 2004;36:1750–60. [DOI] [PubMed] [Google Scholar]
  • 44. Casavale KO, Guenther PM, Reedy J.. The Healthy Eating Index-2010 is a valid and reliable measure of diet quality according to the 2010 Dietary Guidelines for Americans. J Nutr 2013;144:399–407. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 45. Hamilton BE, Hoyert DL, Martin JA, Strobino DM, Guyer B.. Annual summary of vital statistics: 2010–2011. Pediatrics 2013;131:548–58. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 46. Ananth CV, Schisterman EF.. Confounding, causality, and confusion: the role of intermediate variables in interpreting observational studies in obstetrics. Am J Obstet Gynecol 2017;217:167–75. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 47. Zhou XH, Eckert GJ, Tierney WM.. Multiple imputation in public health research. Stat Med 2001;20:1541–49. [DOI] [PubMed] [Google Scholar]
  • 48. Levy-Marchal C, Jaquet D.. Long-term metabolic consequences of being born small for gestational age. Pediatr Diabetes 2004;5:147–53. [DOI] [PubMed] [Google Scholar]
  • 49. Alexander G, Wingate M, Mor J, Boulet S.. Birth outcomes of Asian‐Indian‐Americans. Int J Gynaecol Obstet 2007;97:215–20. [DOI] [PubMed] [Google Scholar]
  • 50. Lee HC, Ramachandran P, Madan A.. Morbidity risk at birth for Asian Indian small for gestational age infants. Am J Public Health 2010;100:820–22. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 51. Foster M, Herulah U, Prasad A, Petocz P, Samman S.. Zinc status of vegetarians during pregnancy: a systematic review of observational studies and meta-analysis of zinc intake. Nutrients 2015;7:4512–25. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 52. Kahleova H, Levin S, Barnard N.. Cardio-metabolic benefits of plant-based diets. Nutrients 2017;9:848.. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 53. Penney DS, Miller KG.. Nutritional counseling for vegetarians during pregnancy and lactation. J Midwifery Womens Health 2008;53:37–44. [DOI] [PubMed] [Google Scholar]
  • 54. Sharma D, Kiran R, Ramnath V, Khushiani K, Singh P.. Iron deficiency and anemia in vegetarian mothers and their newborns. Indian J Clin Biochem 1994;9:100–02. [Google Scholar]
  • 55. Lakin V, Haggarty P, Abramovich DR. et al. Dietary intake and tissue concentration of fatty acids in omnivore, vegetarian and diabetic pregnancy. Prostaglandins Leukot Essent Fatty Acids 1998;59:209–20. [DOI] [PubMed] [Google Scholar]

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