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. Author manuscript; available in PMC: 2025 Aug 1.
Published in final edited form as: Obstet Gynecol. 2024 Jun 27;144(2):223–232. doi: 10.1097/AOG.0000000000005660

Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) Enrollment and Adverse Pregnancy Outcomes Among Nulliparous Individuals

Kartik K Venkatesh 1, Xiaoning Huang 2, Natalie A Cameron 3, Lucia C Petito 2, Jennifer Garner 4,5, Amy Headings 6, Andrew S Hanks 7, William A Grobman 1, Sadiya S Khan 2,8
PMCID: PMC11257805  NIHMSID: NIHMS2002377  PMID: 38935972

Abstract

Objective:

To evaluate the relationship between changes in US Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) enrollment during pregnancy from 2016 to 2019 and rates of adverse pregnancy outcomes (APOs) in US counties in 2019.

Methods:

W conducted a e serial, cross-sectional ecological study at the county-level using US National Center for Health Statistics (NCHS) Natality data from 2016 to 2019 of WIC-eligible nulliparous individuals. The exposure was the change in county-level WIC enrollment from 2016 to 2019 (increase [>0%] versus no change or decrease [≤0%]). Outcomes were APOs assessed in 2019 and included maternal outcomes (i.e., gestational diabetes [GDM], hypertensive disorders of pregnancy [HDP], cesarean delivery, intensive care unit [ICU] admission, and transfusion) and infant outcomes (i.e., large-for-gestational-age [LGA], small-for-gestational-age [SGA], preterm birth [PTB], and NICU admission).

Results:

Among 1,945,914 deliveries from 3,120 US counties, the age-standardized rate of WIC enrollment decreased from 73.1 (95% CI: 73.0 to 73.2) in 2016 to 66.1 (95% CI: 66.0 to 66.2) per 100 live births in 2019, for a mean annual percent change decrease of 3.2% (95% CI: −3.7, −2.9) per year. Compared with counties in which WIC enrollment decreased or did not change, individuals living in counties in which WIC enrollment increased had lower rates of maternal APOs, including GDM (aOR: 0.71; 95% CI: 0.57, 0.89), ICU admission (aOR: 0.47; 95% CI: 0.34, 0.65), and transfusion (aOR: 0.68; 95% CI: 0.53, 0.88); and infant APOs, including PTB (aOR 0.71; 95% CI: 0.56, 0.90) and NICU admission (aOR: 0.77; 95% CI: 0.60, 0.97); but not cesarean delivery, HDP, or LGA or SGA birth.

Conclusions:

Increasing WIC enrollment during pregnancy at the county level was associated with a lower risk of APOs. In an era where WIC enrollment has decreased and food and nutrition insecurity has increased, efforts are needed to increase WIC enrollment among eligible individuals in pregnancy.

Keywords: pregnancy, WIC, adverse pregnancy outcomes, nutrition, food insecurity

PRECIS

Increasing enrollment in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) during pregnancy at the county level was associated with a lower risk of adverse pregnancy outcomes.

INTRODUCTION

Food insecurity is an adverse social determinant of health that includes anxiety about, a lack of resources for, and inadequate access to nutritious food.1,2,3,4 Food insecurity affects 1 in 5 pregnant individuals in the US.5–7 Non-Hispanic Black and Hispanic families are 2 times as likely to report food insecurity compared with non-Hispanic White families.8,9

Pregnant individuals with food insecurity are more likely to experience adverse pregnancy outcomes (APOs), including gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), abnormal gestational weight gain, preterm birth (PTB), and low birthweight.10–16 After pregnancy, food insecurity increases the risk of maternal postpartum depression and diabetes.17,18 Children exposed in utero to food insecurity are at increased risk themselves of obesity, diabetes, and cardiovascular disease later in life.19,20

The main policy tools that aim to reduce food insecurity are federal food assistance programs, and specifically for eligible pregnant individuals and their children, the US Special Supplemental Nutrition Program for Women, Infants, and Children (WIC).3 WIC provides supplemental access to food, nutrition education, breastfeeding support, and screening for medical and social services.21 In 2022, WIC served approximately 600,000 pregnant individuals.22

WIC enrollment may lessen the risk of APOs,23,24 by addressing food and nutrition insecurity and enhancing access to medical, preventative, and social services.25,26 Despite these benefits, WIC enrollment has decreased from 79% of eligible pregnant individuals in 2011 to 68% in 2017.24 Contemporary evidence to examine the population-level impact of such programs over time on APOs is needed given the growing recognition of food insecurity’s negative influence on maternal and child health, the persistence of high rates of food insecurity in pregnancy, and intensified debates regarding federal investment in these programs.27,28 The objective of the current analysis was to evaluate the relationship between changes in WIC enrollment during pregnancy from 2016 to 2019 and rates of APOs in 2019 across the US at the country-level.

METHODS

We conducted a serial cross-sectional analysis at the county-level using the Centers for Disease Control and Prevention National Center for Health Statistics (NCHS) Natality Files from 2016 to 2019. The data were organized at the county-level as WIC is delivered at the community level via 1,900 local agencies; given that WIC is administered and delivered at the local level under broader state oversight and federal guidance, the exposure was defined at the county- rather than state-level. Birth certificate data include all live births in the US, and were collected by birth facilities using standardized maternal and facility worksheets.29 NCHS provided guidance to birth facilities with regard to data abstraction and documentation.29 Demographic, health information, and clinical data were collected by a health information specialist. These data were then reported to state health departments for further data processing and reporting and then to NCHS for federal reporting. This study was deemed exempt by the Northwestern University Feinberg School of Medicine Institutional Review Board Review given that the data were deidentified and publicly available.

We included singleton live births to nulliparous pregnant individuals aged 18 to 44 years who delivered from 2016 to 2019. We excluded parous (i.e., those with a prior birth) individuals because they may have been enrolled in WIC during a previous pregnancy or after their child was born.. This analysis was further restricted to individuals who were deemed to be WIC eligible, defined as those who were US residents and Medicaid insured as a proxy for income eligibility. Individuals whose WIC enrollment status was not recorded were excluded. We used data starting in 2016 because this was the first year that all states adopted the 2003 revised version of the US birth certificate.

The exposure was the change in county-level WIC enrollment during the 4-year period beginning in 2016 and ending in 2019. We measured the change in county-level WIC enrollment as a binary variable: increase [>0%] versus no change or decrease [≤0%]. This analytic approach was taken to allow consistency with exposure categorization in prior epidemiologic studies assessing the association between WIC and APOs, the lack of other established cutoff values to measure changes in WIC enrollment, and the limitations to assess more granular changes in WIC enrollment at the county-level using birth certificate data.23,26,30

Rates of APOs were assessed in 2019 and included maternal outcomes (i.e., GDM, HDP, cesarean delivery, intensive care unit [ICU] admission, and transfusion) and infant outcomes (i.e., large-for-gestational-age [LGA], small-for-gestational-age [SGA], any PTB, and NICU admission). These outcomes were selected a priori based on data available in the birth certificate and to be consistent with a recent systematic review and meta-analysis of the association between WIC enrollment and APOs.23,26 HDP included gestational hypertension, preeclampsia, and eclampsia.31 Maternal and neonatal ICU admissions included admissions to an ICU for any clinical indication during the delivery hospitalization. Maternal transfusion was defined as any blood product administered during the delivery hospitalization. LGA was defined as a standardized birthweight ≥90th percentile, and SGA as <10th percentile using a revised birthweight-for-gestational age reference for the US based on obstetric criteria for pregnancy dating.32 Preterm birth was defined as any birth <37 weeks of gestation regardless of clinical indication.

We also assessed demographic characteristics, such as age at delivery, self-reported race and ethnicity, educational attainment, and timing of initiating prenatal care. We examined race and ethnicity as a social construct because minoritized subgroups are more likely to experience food insecurity due to structural racism, which was self-identified on the maternal worksheet as: Hispanic, non-Hispanic Asian-Pacific Islander, non-Hispanic Black, non-Hispanic American Indian, or non-Hispanic White.33,34 We employed bridged-race categories due to differences in state-level categorization to allow for comparisons of race-specific statistics over time.35 We also assessed US census region (Midwest, Northeast, South, and West) and urbanicity status (urban and rural) using the 2013 NCHS county-level urban-rural classification at the county-level based on the pregnant individual’s legal residence at the time of birth.

We calculated the age-standardized frequency of WIC enrollment as a percentage per year (i.e., the number of enrolled individuals per 100 deliveries). We assessed the change in WIC enrollment as the mean annual percent change (APC) overall and by two place-based social determinants of health, US region and urbanicity status. To calculate the mean APC, we used Joinpoint Regression statistical software, version 4.7.0, which accounts for potential nonlinear trends by inflection points, and identifies nonlinear trends by weighting for the trend segment.36 To compare mean APC estimates between subgroups, we assessed whether the 95% confidence interval (CI) for each subgroup overlapped, with non-overlapping CIs considered to indicate differences that were statistically significant (p<0.05).

To examine the association between county-level WIC enrollment and APOs, we used hierarchical logistic regression to account for both county- and individual-level covariates and clustered on US state, and calculated unadjusted and adjusted odds ratios (ORs, aORs). Covariates were selected for inclusion in the multivariable model a priori based on a directed acyclic graph and prior studies assessing WIC enrollment in pregnancy (Appendix 1, available online at http://links.lww.com/xxx). The final model adjusted for: 1) the baseline county-level mean WIC enrollment in 2016, 2) the baseline county-level rate for the corresponding APO in 2016, and 3) socio-demographic covariates measured at the county-level across the study period, including mean age at delivery, and the proportion of individuals at the county-level that self-identified as non-Hispanic White, completed college education or greater, and enrolled in prenatal care in the first trimester. Missing data for covariates were represented in the model with a categorical-variable term rather than as imputed values, given the low frequency of missing values and consistent with prior analyses using vital statistics data.

In interaction analyses, we assessed whether the association between WIC and APOs varied by county-level subgroups, including US census region (Midwest, Northeast, South, and West) and urbanicity status (rural and urban) to account for effect modification by these place-based social determinants of health. We provided analyses stratified by these two county-level covariates (US region and urbanicity) if the interaction term in the multivariable model was statistically significant (p<0.05). These models to assess for interaction effects were adjusted for the same covariates as the primary analysis above. All statistical analyses were performed using Stata version 16.1 (StataCorp LLC), and software available from the National Cancer Institute (Surveillance, Epidemiology, and End Results Online Age Period Cohort Analysis Tool).37

RESULTS

Among 15,145,230 live births in the US from 2016 to 2019, we excluded non-US residents (N=38,506), multiparous individuals (N=9,495,818), individuals not enrolled in Medicaid (N=3,641,587), and individuals missing WIC enrollment status (N=23,405), resulting in a final analytic sample of 1,945,914 deliveries from 3,120 US counties (Appendix 2, available online at http://links.lww.com/xxx).

Among the study population, the mean age was 24.0 years (standard deviation: 4.9), 84.3% had at least a high school education, and 68.2% initiated prenatal care in the first trimester (Table 1). Five percent of individuals self-identified as Asian, 21.9% as Black, 31.0% as Hispanic/Latina, 1.0% as American Indian, and 38.0% as White. Sixteen percent of individuals lived in rural areas and 84.5% in urban areas. Over two-fifths (44.3%) of individuals lived in the South, 17.8% in the Midwest, 15.1% in the Northeast, and 22.8% in the West.

Table 1.

Characteristics of WIC-eligible nulliparous individuals overall and by county-level change in WIC enrollment

Overall No change/ decreased WIC enrollment Increased WIC enrollment
n (%) n (%) n (%)
N=1,945,914 N=1,749,519 N=196,395
Age, years, mean (SD) * 24.0 (4.9) 24.1 (5.0) 23.4 (4.6)
Age group, years *
 18–19 339,307 (17.4) 299,662 (17.1) 39,645 (20.2)
 20–24 868,760 (44.6) 775,239 (44.3) 93,521 (47.6)
 25–29 458,997 (23.6) 417,600 (23.9) 41,397 (21.1)
 30–34 194,220 (10.0) 178,741 (10.2) 15,479 (7.9)
 35–39 70,341 (3.6) 64,999 (3.7) 5,342 (2.7)
 40–44 14,289 (0.7) 13,278 (0.8) 1,011 (0.5)
Race and ethnicity *
 Non-Hispanic Asian/Pacific Islander 91,379 (4.7) 86,449 (4.9) 4,930 (2.5)
 Non-Hispanic American Indian 19,448 (1.0) 15,644 (0.9) 3,804 (1.9)
 Hispanic 602,532 (31.0) 558,797 (31.9) 43,735 (22.3)
 Non-Hispanic White 740,058 (38.0) 635,085 (36.3) 104,973 (53.4)
 Non-Hispanic Black 426,412 (21.9) 394,314 (22.5) 32,098 (16.3)
 Additional races and ethnicities 66,085 (3.4) 59,230 (3.4) 6,855 (3.5)
US region *
 Midwest 346,501 (17.8) 298,000 (17.0) 48,501 (24.7)
 Northeast 293,794 (15.1) 277,810 (15.9) 15,984 (8.1)
 South 862,287 (44.3) 784,226 (44.8) 78,061 (39.7)
 West 443,332 (22.8) 389,483 (22.3) 53,849 (27.4)
Urbanity *
 Rural 301,909 (15.5) 227,257 (13.0) 74,652 (38.0)
 Urban 1,644,005 (84.5) 1,522,262 (87.0) 121,743 (62.0)
Education *
 Less than high school 306,184 (15.7) 275,061 (15.7) 31,123 (15.8)
 High school or some college 1,310,083 (67.3) 1,172,890 (67.0) 137,193 (69.9)
 Bachelor's or associate's degree 270,316 (13.9) 246,292 (14.1) 24,024 (12.2)
 Master's or doctorate degree 38,768 (2.0) 36,065 (2.1) 2,703 (1.4)
 Not reported 20,563 (1.1) 19,211 (1.1) 1,352 (0.7)
Initiation of prenatal care *
 First trimester 1,326,944 (68.2) 1,189,511 (68.0) 137,433 (70.0)
 Second trimester 413,855 (21.3) 373,167 (21.3) 40,688 (20.7)
 Third trimester or no care 154,202 (7.9) 139,745 (8.0) 14,457 (7.4)
 Not reported 50,913 (2.6) 47,096 (2.7) 3,817 (1.9)
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*

p<0.01 for all comparisons by county-level change in WIC enrollment.

Individuals living within counties in which WIC enrollment increased were significantly younger; were less likely to self-identify as Black, Hispanic, or Asian, and more likely to self-identify as White and American Indian; were more likely to be from the Midwest and West and less likely to be from the Northwest or South; were more likely to be from rural communities; were more likely to have a lower level of educational attainment; and were more likely to enroll in prenatal care earlier in pregnancy (p<0.01 for all) (Table 1).

The mean county-level WIC enrollment was 74.2% (SD: 16.8%) in 2016. The mean county-level WIC enrollment in 2016 in counties in which enrollment increased was 66.5% (SD: 19.9%) and 77.0% (SD: 14.7%) in counties in which enrollment decreased or did not change. In 2016, 15.4% of counties had ≥90% of eligible individuals enrolled in WIC, 28.6% of counties had between ≥75% to 90% of eligible individuals enrolled in WIC, 41.6% of counties had between ≥60% to <75% of eligible individuals enrolled in WIC, and 14.5% of counties had <60% of eligible individuals enrolled in WIC (Figure 1a) (Appendix 3, available online at http://links.lww.com/xxx).

Figure 1.

Figure 1.

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(A) County-level Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) enrollment in 2016.Overall distribution of country-level WIC enrollment in 2016 is shown in Appendix 3. (B) County-level Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) enrollment in 2019. Overall distribution of country-level WIC enrollment in 2019 is shown in Appendix 4. (C) Change in county-level Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) enrollment between 2016 and 2019.

In comparison, the mean county-level WIC enrollment was 67.5% (SD: 18.7%) in 2019. The mean county-level WIC enrollment in 2019 in counties in which enrollment increased was 76.8% (SD: 17.9%) and 64.1% (SD: 17.8%) in counties in which enrollment decreased or did not change. In 2019, 9.3% of counties had ≥90% of eligible individuals enrolled in WIC, 29.4% of counties had between ≥75% to 90% of eligible individuals enrolled in WIC, 33.1% of counties had between ≥60% to <75% of eligible individuals enrolled in WIC, and 28.2% of counties had <60% of eligible individuals enrolled in WIC (Figure 1b) (Appendix 4, available online at http://links.lww.com/xxx).

The mean change in county-level WIC enrollment overall during the study time period was −6.5% (SD: 17.5%). The mean change in county-level WIC enrollment in counties in which WIC enrollment increased was 11.9% (SD: 14.4%) and was −12.9% (SD: 13.5%) in counties in which enrollment decreased or did not change. WIC enrollment increased in 27.4% of counties from 2016 to 2019, and decreased or did not change in the remaining 72.6% of counties (Figure 1c).

The age-standardized rate of WIC enrollment decreased from 73.1 (95% CI: 73.0 to 73.2) in 2016 to 66.1 (95% CI: 66.0 to 66.2) per 100 live births in 2019, for a mean APC decrease of 3.2% (95% CI: −3.7, −2.9) per year. The decrease in WIC enrollment was similar across both urban and rural areas and all US regions (Table 2).

Table 2.

Age-Standardized Rate and mean Annual Percent Change (APC) in the frequency of county-level WIC enrollment from 2016 to 20191

2016 2019 Change from 2016 to 2019
N Crude Rate (%) Age-Standardized Rate
% (95% CI)		 N Crude Rate (%) Age-Standardized Rate
% (95% CI)		 Mean APC
OVERALL 504,365 73 73.1 (73, 73.2) 468,088 66 66.1 (66, 66.2) −3.2 (−3.7, −2.9)
BY SUBGROUP
US region
Midwest 90,617 71 69.9 (69.6, 70.2) 82,255 64 63.4 (63.1, 63.7) −3.2 (−3.6, −3)
Northeast 74,993 70 71.6 (71.3, 71.9) 70,488 62 63.9 (63.5, 64.3) −3.5 (−4.4, −2.7)
South 220,600 76 75.4 (75.2, 75.6) 212,359 69 68.3 (68.1, 68.5) −3.2 (−4.1, −2.4)
West 118,155 72 72.3 (72.0, 72.6) 102,986 65 65.5 (65.2, 65.8) −3.1 (−3.7, −2.6)
Urbanicity
Rural 78,944 79 77.4 (77.1, 77.7) 72,122 73 71.7 (71.4, 72) −2.5 (−3.5, −1.6)
Urban 425,421 72 72.3 (72.2, 72.4) 395,966 65 65.1 (65.0, 65.2) −3.4 (−3.7, −3.1)
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1

Age-standardized rates are based on the age group distribution in 2016.

Compared with counties in which WIC enrollment decreased or did not change, individuals living in counties in which WIC enrollment increased had significantly lower rates of maternal APOs in 2019 (after adjustment for covariates, including baseline WIC enrollment and baseline APO frequency), including GDM (aOR: 0.71; 95% CI: 0.57, 0.89), ICU admission (aOR: 0.47; 95% CI: 0.34, 0.65), and transfusion (aOR: 0.68; 95% CI: 0.53, 0.88)] (Table 3). Similarly, individuals living in counties in which WIC enrollment increased had significantly lower rates of infant APOs in 2019, including PTB (aOR 0.71; 0.56, 0.90) and NICU admission (aOR: 0.77; 95% CI: 0.60, 0.97), compared with those living in counties in which WIC enrollment decreased or did not change. Changes in WIC enrollment were not associated with the adjusted odds of cesarean delivery, HDP, or LGA or SGA at birth.

Table 3.

Association between county-level change (increase versus no change or decrease) in WIC enrollment and adverse pregnancy outcomes1

Frequency of outcomes by WIC enrollment status Unadjusted analysis Adjusted analysis
No change or decrease Mean % (10th%tile, 90thtile) Increase Mean % (10th%tile, 90thtile) Unadjusted odd ratios, OR (95% CI)2 Adjusted odd ratios, AOR (95% CI)2,3 Adjusted odds ratio, AOR (95% CI)2,3,4
Maternal outcomes
Cesarean delivery 28.5 (15.8, 40.9) 27.9 (9.5, 43.1) 0.56 (0.37, 0.85)* 0.90 (0.59, 1.37) 1.00 (0.68, 1.48)
HDP 10.7 (0.0, 19.2) 11.1 (0.0, 20.3) 0.59 (0.45, 0.76)* 0.78 (0.58, 1.04) 0.83 (0.62, 1.12)
GDM 5.4 (0.0, 11.1) 5.3 (0.0, 12.5) 0.56 (0.48, 0.67)* 0.65 (0.52, 0.80)* 0.71 (0.57, 0.89)*
ICU admission 0.2 (0.0, 0.4) 0.2 (0.0, 0.0) 0.47 (0.35, 0.63)* 0.42 (0.30, 0.58)* 0.47 (0.34, 0.65)*
Transfusion 0.6 (0.0, 1.7) 0.8 (0.0, 2.1) 0.62 (0.50, 0.77)* 0.62 (0.48, 0.80)* 0.68 (0.53, 0.88)*
Infant outcomes
PTB 3.7 (0.0, 7.8) 3.2 (0.0, 7.8) 0.54 (0.44, 0.65)* 0.64 (0.51, 0.80)* 0.71 (0.56, 0.90)*
NICU admission 9.2 (0.0, 16.7) 8.6 (0.0, 18.2) 0.55 (0.45, 0.68)* 0.70 (0.55, 0.89)* 0.77 (0.60, 0.97)*
LGA 8.6 (0.0, 15.0) 8.7 (0.0, 16.7) 0.58 (0.46, 0.75)* 0.76 (0.57, 1.00)* 0.84 (0.63, 1.11)
SGA 16.8 (5.3, 26.4) 16.5 (0.0, 28.6) 0.62 (0.46, 0.83)* 0.87 (0.62, 1.23) 0.98 (0.67, 1.42)
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1

Exposure measured change in WIC enrollment from 2016 to 2019. Outcomes ascertained in 2019.

2

Hierarchical logistic regression was used, hierarchically clustered on U.S. state.

3

Adjusted for 1) county-level WIC enrollment in 2016; and 2) county-level rate of the adverse pregnancy outcome in 2016.

4

Adjusted for 1) county-level WIC enrollment in 2016; 2) county-level rate of the adverse pregnancy outcome in 2016; and 3) socio-demographic covariates measured at the county-level across the study period, including mean age at delivery, and the proportion of individuals at the county-level that self-identified as non-Hispanic White, completed college education or greater, and enrolled in prenatal care in the first trimester.

*

p<0.05.

Abbreviations: Hypertensive disorders of pregnancy (HDP), gestational diabetes (GDM), intensive care unit (ICU), preterm birth (PTB), neonatal intensive care unit (NICU), large-for-gestational-age (LGA), and small-for-gestational-age (SGA).

The association between the change in WIC enrollment from 2016 to 2019 and APOs in 2019 varied by urbanicity status for several outcomes (i.e., interaction p-values <0.05 for GDM, transfusion, and NICU admission). Specifically, in urban areas, increasing WIC enrollment was associated with a lower rate of GDM, transfusion, and NICU admission compared with decreasing or no change in WIC enrollment (Appendix 5, available online at http://links.lww.com/xxx). However, in rural areas, there was no significant association between WIC enrollment and APOs. The association between changes in WIC enrollment and APOs did not vary by US region (interaction p-value ≥0.5 for all outcomes) (Appendix 6, available online at http://links.lww.com/xxx).

DISCUSSION

US counties that experienced an increase in WIC enrollment between 2016 to 2019 had a lower likelihood of maternal APOs, including GDM, ICU admission, transfusion, as well as infant APOs, including NICU admission and PTB, compared with those counties in which WIC enrollment decreased or did not change.

This longitudinal ecological analysis provides estimates of the potential population-level impact of changes in WIC enrollment over time on multiple measures of maternal and infant morbidity. These longitudinal findings are consistent with a recent systematic review of 20 primarily cross-sectional studies on the association between WIC enrollment and the risk of birth outcomes, including preterm birth, low birthweight, and infant mortality.23 The observed magnitude of risk reduction in the current analysis was generally higher than those observed in these prior cross-sectional analyses. In addition, the current study included a broader set of adverse infant and maternal outcomes than have previously been investigated,26 including measures of maternal morbidity. Finally, the current study assessed the community as opposed to individual-level impact of WIC enrollment on APOs using an ecological analytic framework. Due to the study design, it is possible that unmeasured factors affected pregnancy outcomes and changes in county-level WIC enrollment.

In the current longitudinal and community-level analysis, increasing WIC enrollment over time was associated with a decreased risk of PTB and NICU admission, which is consistent with a prior cross-sectional and individual-level analyses.24,38 The current study did not find an association between increasing WIC enrollment and SGA or LGA birth, while prior analyses suggested that WIC enrollment was associated with a lower risk of low birthweight.39–41 Unlike the current study that used standardized gestational age corrected measures to assess birthweight, prior studies assessed birthweight as a continuous measure without standardization.

Increasing WIC enrollment was associated with fewer adverse maternal outcomes, such as GDM and markers of severe maternal morbidity, including ICU admission and transfusion; however, not with cesarean delivery nor HDP. A prior study found that the revised WIC food package implemented in 2009 was associated with a reduced rate of HDP and excess gestational weight gain.42 Otherwise, prior studies generally have not assessed the impact of WIC enrollment on maternal morbidity.23 With regards to other federal programs, state-level Medicaid expansion has been associated with reduced maternal mortality.43

The impact of increasing WIC enrollment on APO prevention was not uniformly observed across rural and urban communities. In rural communities, where rates of WIC enrollment were higher compared with urban communities, there was no significant association between increasing WIC enrollment and APOs. However, these exploratory analyses may be limited due to the smaller sample size of the strata. Pregnant individuals in rural areas are more likely to have comorbid medical conditions and APOs,44,45 and experience a higher burden of unmet social needs.46 Further efforts to improve uptake of WIC services in rural communities may be needed.

The exact pathways through which increasing WIC participation may result in population-level changes in APOs requires further study. Possible mechanisms include improvements in diet quality and nutrition intake through nutrition education and the provision of supplemental foods.47 In addition, WIC enrollment may be associated with improved access to and timing of prenatal care and concurrent enrollment in other programs that address non-medical social needs.43,48

With regards to policy implications, these data support efforts aimed at increasing WIC enrollment and utilization. The proportion of WIC-eligible individuals who enrolled decreased during the study period,24 albeit recent data suggest that enrollment is starting to increase.49 Possible reasons for low WIC enrollment include logistical barriers, limited selection of WIC-eligible foods and products,50 and restrictive enrollment criteria.51 Interventions that have resulted in increases in WIC enrollment include online or virtual engagement and addressing transportation-related barriers to access.30,52,53,54 The future of WIC funding remains a cause for concern.55 Some congressional bills currently under consideration could cut WIC funding, while others include provisions to enhance postpartum WIC eligibility. The impact of these competing policy objectives could have long-term consequences for maternal and child health.

There are several study limitations to note. First, the exposure was assessed as a dichotomous variable of “increase” versus “no change or decrease” in WIC enrollment for several reasons, including: consistency with prior analyses, the lack of established cutoff values, the inability to assess for more granular changes in WIC enrollment at the county-level using birth certificate data,23,26,30 and because the amount of change in WIC enrollment had a relatively compressed range across assessed counties. Nevertheless, even with our dichotomized exposure, an association was observed. Second, this analysis was restricted to 2016 to 2019. Prior to 2016, not all states had implemented the 2003 revision of the birth certificate. After 2019, the COVID-19 pandemic may have affected the rate of WIC enrollment as well as APOs.49 Third, birth certificate data ascertain WIC enrollment, but not the degree to which WIC benefits were used during pregnancy. Fourth, this analysis included live births and excluded pregnancies that could have resulted in miscarriage or stillbirth. Fifth, this analysis did not elucidate the mechanisms by which WIC enrollment resulted in differences in pregnancy outcomes. Sixth, assessment of WIC enrollment at the county level even after adjustment for county-level covariates may not account for unobserved individual- and county-level characteristics. Seventh, this analysis was limited to APOs that were collected in the birth certificate. Eighth, this analysis used Medicaid enrollment as a proxy for income eligibility for WIC. However, some individuals at high risk for APOs, such as those without legal documentation, recent immigrants, and refugees, may not be enrolled in Medicaid but may be eligible for WIC. Finally, this analysis may not be generalizable to all WIC enrolled pregnant individuals as this analysis was restricted to nulliparous individuals.

In conclusion, from 2016 to 2019 across the US, as a greater proportion of eligible nulliparous individuals within a county enrolled in WIC, the likelihood of maternal and infant APOs decreased. These data provide evidence of the potential value of WIC to decrease maternal and neonatal morbidity, and of efforts to increase WIC enrollment in pregnancy.

Supplementary Material

Supplemental Digital Content_1
Supplemental Digital Content_2

Funding:

The Care Innovation and Community Improvement Program at The Ohio State University (Dr. Venkatesh) and NHLBI grant #HL161514 (Dr. Khan).

Footnotes

Financial Disclosure

Lucia C. Petito reported that money was paid to her institution from Omron Healthcare Co., Ltd. The other authors did not report any potential conflicts of interest.

Each author has confirmed compliance with the journal’s requirements for authorship.

Presented at the Society for Maternal-Fetal Medicine 44th Annual Meeting in February 11–14, 2024, National Harbor, MD.

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