In the United States, rate of preterm birth peaked in 2006 and little progress has been made to date despite ambitious Healthy People 2020 goals. Infants born premature are at higher risk of death and disability, including psychological conditions, learning difficulties and medical disabilities, than term newborns. Additionally, adverse birth outcomes are associated with asthma, the leading cause of chronic childhood illness and disability. According to the ‘Barker hypothesis’, intrauterine exposures may serve as a programming stimulus that alters the development of biologic systems and the risk or susceptibility to future disease. One such programming stimulus is maternal nutrition in pregnancy as previous research has shown associations between prenatal nutrition (such as vitamin supplement use and Special Supplemental Nutrition Program for Women, Infants and Children enrollment (WIC)) and birth and early childhood respiratory health outcomes. Through this dissertation, we address gaps in knowledge regarding supplement use in pregnancy and prenatal enrollment in the nutrition program among low-income, minority women, allowing for better informed public health messages.
In the first study, we identified WIC eligible parous women who gave birth to first and second siblings between 2007 and 2011 from California electronic birth records to assess the impact of program enrollment on recurrent preterm birth. WIC eligibility in the second pregnancy was based upon both an income criteria (assessed through Medi-Cal as the second pregnancy primary payer for prenatal care) and “nutritional risk” (assessed through a premature first birth). We found that eligible second pregnancy non-enrollees had a higher risk of recurrent preterm birth than program participants among both first pregnancy WIC non-enrollees and first pregnancy WIC enrollees. These findings suggest that the benefits provided by WIC to patrons, including vouchers for food supplementation, counseling and referrals to health and social services, may improve birth outcomes of the women electing to enroll in the program. In sensitivity analyses, we also found the magnitude of this association was strongest for the following high risk subgroups of eligible women: first pregnancy Medi-Cal participants, younger, and Black or Hispanic mothers with the shortest time between births.
The second study used data from a Los Angeles based case-control study nested within the 2003 birth cohort to assess the relationship between the timing of pre-natal supplement initiation and birth outcomes. This study limited analyses to non-Hispanic white and Hispanic women, the predominant racial/ethnic groups among respondents. Among Hispanic mothers, we observed an increased odds of preterm birth the later a woman initiated pre-natal supplement use in pregnancy and the magnitude of the association was larger in US-born compared to foreign-born women. The case-control respondents were followed approximately three years later to assess offspring respiratory outcomes. The third study objective was to assess whether adverse early childhood respiratory health is associated with the timing of folic acid supplement initiation in pregnancy. Among all study participants, timing of folic acid use (derived from reports of both folic acid and pre-natal supplements) was not associated with wheeze in the first three years of life, current wheeze, or lower respiratory tract infection in offspring even after re-weighing the population to account for premature birth and censorship. Among mothers with a history of eczema, hay fever or asthma, we found late folic acid supplement initiators had between 1.7-1.9 times the risk of adverse respiratory health outcomes compared to their first trimester initiating counterparts. No association was found among non-atopic mothers.
In conclusion, our results support that prenatal nutrition in pregnancy may serve as a programming stimulus as timing of supplement initiation and nutrition program enrollment were found to be associated with offspring health. Both are potentially modifiable factors and the information obtained through these studies highlights the importance of tailored public health interventions for those at highest risk of adverse birth and childhood respiratory health outcomes.
