Maternal diet before and during pregnancy may play an important role in maternal, neonatal, and child health outcomes [1
]. Specifically, pregnant women require additional folate and iron before and during pregnancy to meet their own needs and optimize birth outcomes [3
]. Preterm birth and low birth weight have been associated with inadequate folate intake [4
] and iron deficiency during pregnancy [5
]. In the United States, women of childbearing age who are overweight or obese had lower serum concentrations of folate compared to those women with underweight and normal weight [6
]. Adverse birth outcomes have been associated with pre-pregnancy overweight and obesity and inadequate maternal nutrition during pregnancy.
Overweight and obesity status before pregnancy has been found to be associated with excessive gestational weight gain [7
], which in turn is associated with postpartum weight retention [8
]. Pre-pregnancy weight status has also been reported as an independent determinant for gestational diabetes mellitus, gestational hypertension, preterm birth, and small and large for gestational age births in U.S. pregnant women [9
]. Diet during pregnancy may partially mediate the relationship between pre-pregnancy overweight and obesity and pregnancy complications and birth outcomes [10
]. Laraia et al.
] first demonstrated that pre-pregnancy BMI was inversely associated with diet quality as measured by the Diet Quality Index for Pregnancy (DQI-P) in pregnant women in North Carolina. In a cross-sectional study of Greek women, Tsigga et al.
] also reported that pregnant women who were underweight or normal weight before pregnancy demonstrated a better diet quality as assessed by the Healthy Eating Index (HEI)-2005 compared to women with obese pre-pregnancy BMI. However, the majority of the study population in these studies [11
] were low- to middle-income non-Hispanic white women. Thus, this may not be representative of the entire population of U.S. pregnant women.
Gestational weight gain guidelines were established by the Institute of Medicine for the optimal health outcomes for the mother and the offspring [13
]. The guidelines are based on pre-pregnancy weight status as the obesity epidemic has been increasing among reproductive aged women in the United States [13
]. It is unclear how pre-pregnancy weight status is associated with gestational weight gain through maternal diet during pregnancy. Diet during pregnancy may play a significant role linking the association between pre-pregnancy weight status and gestational weight gain. Recently, Graziano et al.
] found that HEI-2010 may provide useful information assessing overall diet quality during pregnancy. It is important to examine the relationship between pre-pregnancy weight status and diet quality assessed by HEI-2010 and nutritional biomarkers including serum folate, iron, and ferritin concentrations during pregnancy in U.S. representative pregnant women.
Pregnant women included in this study were 52% non-Hispanic white, 23% Mexican American or other Hispanic, 18% non-Hispanic black, and 8% other race; 64% were married; and 91% had between 1 and 5 previous live births. Forty-four percent had an income of <185% of the poverty level (the income eligibility criterion for the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC)). Fifty-nine percent had more than a college level education, 39% were in their third trimester of pregnancy, 9% were smokers during pregnancy, and 35% engaged in light leisure-time physical activities during pregnancy (Table 2
For all pregnant women included in this study, the mean HEI-2010 (±standard error of the mean (SEM)) was 50.7 (±0.9). The mean HEI-2010 score varied significantly by maternal sociodemographic characteristics (Table 2
). Significantly higher mean HEI-2010 scores were found for pregnant women who were older than 35, other race including multi-racial groups, family poverty income ratio above 4, married, and non-smokers. Multi-collinearity between age, race/ethnicity, family poverty income ratio, education, marital status, parity number, trimester of pregnancy, smoking status, and physical activity were assessed. The VIF for all the confounding variables ranged from 1.04 to 1.59. These findings suggest that collinearity between these confounding variables was not significant.
shows covariate-adjusted mean HEI across all the pre-pregnancy weight status groups. After adjusting for maternal age, race/ethnicity, family poverty income ratio, education, marital status, smoking status and physical activity, women with obese pre-pregnancy BMI had significantly lower overall HEI-2010 compared to those with normal pre-pregnancy BMI (48.8 ± 2.0 vs.
55.2 ± 1.6). Women with obese pre-pregnancy BMI had significantly lower scores for the sodium component compared to normal weight women (3.7 ± 0.6 vs.
5.4 ± 0.4) (Table 3
represents mean values for dietary intake and diet-related biomarkers across pre-pregnancy weight status groups. Intakes of folate (mcg)/1000 kcal and iron (mg)/1000 kcal significantly differed by pre-pregnancy weight status. Women of obese pre-pregnancy BMI had significantly lower intake of both folate and iron per 1000 kcal compared to women of underweight pre-pregnancy BMI. Serum folate (ng/mL) and iron (ug/dL) concentrations were significantly differed by pre-pregnancy weight status groups. Serum folate concentration was significantly higher in underweight women compared to overweight women (23.4 ± 1.7 vs.
17.0 ± 1.8 ng/mL). Serum iron concentration was significantly higher in normal weight women compared to overweight women (86.2 ± 5.0 vs.
68.9 ± 3.0 ug/dL). Folic acid, iron, zinc, and calcium intakes from dietary supplements did not differ by pre-pregnancy weight status (Table 4
In the unadjusted logistic regression analysis, results show that women with pre-pregnancy overweight and obese BMI had increased odds of falling into the lowest (mean 33.4 ± SEM 0.5) vs.
the highest (mean 66.5 ± SEM 0.9) HEI-2010 tertile compared with underweight BMI (OR 2.6; 95% CI 1.1–6.4, OR 5.0; 95% CI 2.2–11.4, respectively) (Table 5
). We then compared two models controlling first for maternal age, race/ethnicity, family poverty income ratio, education level, marital status, and smoking status. In the second model, we controlled for the covariates controlled in the first model as well as leisure-time physical activity level during pregnancy. The inverse association between pre-pregnancy overweight and obesity and diet quality during pregnancy remained significant after we adjusted for maternal characteristics (adjusted OR (AOR) 2.8; 95% CI 1.2–6.6, AOR 3.7; 95% CI 1.7–8.2). The inverse association between pre-pregnancy overweight and obesity and diet quality persisted even after we controlled for physical activity levels (AOR 3.8; 95% CI 1.2–11.7, AOR 5.4; 95% CI 2.0–14.5) (Table 5
Recently, HEI-2010 has been reported to be valid and reliable in assessing the overall diet quality of an individual in terms of conforming to federal dietary guidance [31
]. However, Pick et al.
] reported that the HEI was useful in providing a composite measure of dietary intake, but did not discern the need for vitamin and mineral supplements during pregnancy. To overcome this issue, we examined folate, iron, and calcium from both a dietary recall and their biomarker values across pre-pregnancy weight status. Serum folate concentration decreased as pre-pregnancy BMI increased, as others have found [33
]. Serum folate concentration was significantly higher in underweight women compared to overweight women in our study (23.4 ± 1.7 vs.
17.0 ± 1.8 ng/mL); the mean values in overweight women was within the normal reference range of serum folate, 0.8 to 20.7 ng/mL for pregnant women [34
]. Serum iron concentration was significantly higher in normal weight women compared to overweight women (86.2 ± 5.0 vs.
68.9 ± 3.0 ug/dL), all within the normal reference range of serum iron, 30 to 193 ug/dL for pregnant women [34
]. Because mean serum folate and iron concentrations were all within normal reference ranges in all pre-pregnancy weight status groups, the differences may not be clinically relevant.
This study showed that diet quality during pregnancy measured using HEI-2010 was inversely associated with increasing pre-pregnancy BMI. Our study findings are in agreement with previous research results from Greece [12
] and the United States [11
]. In a cross-sectional study of Greek women [12
], those who were underweight or had a normal pre-pregnancy BMI had a better diet quality as assessed by HEI-2005 compared to those who had an obese pre-pregnancy BMI. Consistent with this finding, in a prospective cohort study in North Carolina, pre-pregnancy BMI was inversely associated with diet quality, as assessed by the DQI-P [11
]. Women who were obese before pregnancy had 76% increased odds of falling into the lowest tertile of diet quality indicated by DQI-P (mean 42, standard deviation 7.2) than those who were underweight before pregnancy. The major difference in our study compared to these two studies [11
] is that we used the most current index (HEI-2010) while others used older versions, HEI-2005 and DQI-P. The updated HEI-2010 was chosen to assess the diet quality of pregnant women in the present study, for it reflects the most current 2010 Dietary Guidelines for Americans with key changes, such as the additional recommendations for seafood (fish and shellfish) and plant proteins, polyunsaturated and monounsaturated fatty acids, and limitations on refined grains [35
In our study, the four most lacking components based on HEI-2010 scores for pregnant women’s diets were greens and beans, whole fruit, whole grains, and seafood and plant proteins. Strategies are needed to recommend greater consumption of greens and beans, whole fruit, whole grains, and seafood and plant proteins among pregnant women to improve overall diet quality. Food pricing strategies such as subsidies on fruits and vegetable and imposing taxes on carbonated drinks were associated with better diet quality and healthier food choices [36
In our study, pregnant women who were older, of another race including the multi-racial group, married, non-smokers, and/or who had high income and high education levels had better diet quality. Our results confirm previous findings that pregnant women with advanced maternal age [37
], high income [37
], and high education [38
] consumed diets of better quality. There are inconsistent findings for the association between race/ethnicity and diet quality during pregnancy. In our study, we found that non-Hispanic black pregnant women demonstrated the lowest HEI-2010 score compare to other race groups. Rifas-Shiman et al.
] reported that African-American pregnant women had similar Alternate HEI-Pregnancy scores assessed in the second trimester of pregnancy compared to other race/ethnicity groups (59.4 ± 10.7 vs.
61.0 ± 10.0, respectively) in the prospective cohort study, Project Viva, after controlling for education and age. Bodnar et al.
] also found no significant ethnic/race differences in mean DQI-P score measured in the second trimester of pregnancy among pregnant women who participated in the Pregnancy, Infection, and Nutrition study. This contradictory finding may be due to a different categorization of race/ethnicity groups. The Pregnancy, Infection, and Nutrition study [37
] categorized race/ethnicity into white and black only, and Project Viva study [38
] categorized race/ethnicity into black/African American, other, and white as the majority of the study population (72%). Our study stratified race/ethnicity into Mexican American or other Hispanic, non-Hispanic white, non-Hispanic Black, and other including multi-racial groups with even distributions across the race/ethnicity categories.
Dietary patterns during pregnancy have been associated with pregnancy complications and birth outcomes. In a prospective cohort study in Sweden [40
], pregnant women who adhered to a “prudent” or “traditional” dietary pattern during pregnancy, characterized by high intake of vegetables, fruit, whole grains, and fish, were at lower risk of preterm birth. In a cross-sectional study of U.S. pregnant women [41
], high consumption of added sugars and low consumption of fruits and vegetables during pregnancy were associated with increased risk for gestational diabetes mellitus. Maternal nutrition plays an important role in pregnancy complications and birth outcomes.
There are several limitations of this study. Due to cross-sectional study design in the NHANES, a cause–effect relationship cannot be made. The study focused on generating snapshots of the diet quality derived from foods and nutrients, and this information may not be adequate to represent the usual dietary intake of pregnant women. In assessing diet intake, one 24-h recall used in this study may not accurately estimate the habitual dietary intake of an individual. In addition, dietary underreporting by overweight and obese women could have resulted in obscured or confounded results in terms of the relationship between diet and weight status [42
]. Dietary supplement use information was assessed using the Dietary Supplement Questionnaire as a part of the 24-h dietary recall interviews. The Dietary Supplement Questionnaire was used to collect information on the participant’s use of vitamins and minerals over the past 30 days. A limited number of pregnant women self-reported their use of dietary supplement. The association between biomarker concentrations and dietary supplement use could have been influenced by the weight status of the responders. Despite these limitations, the study has several strengths. First, we used a validated and reliable index, HEI-2010 [21
], to assess the diet quality of representative U.S. pregnant women in addition to various maternal diet-related biomarkers and intake of supplement across the categories of pre-pregnancy weight status. Second, the study was based on representative U.S. pregnant women incorporating diverse groups of pregnant women in different months of pregnancy. Third, although the study used self-reported pre-pregnancy weight status, we previously validated self-reported pre-pregnancy weight status based on self-reported height and weight before pregnancy, and it was found to be valid [18
]. Lastly, we were able to control for important maternal sociodemographic characteristics, such as smoking status and physical activity level during pregnancy, that may influence the relationship between pre-pregnancy weight status and diet quality.