(PTFS11-01-25) The Interactive Effect of Prenatal Vitamin D Status and Maternal Obesity on Birth Outcomes among US Black Women

Objectives: US Black women have higher risks for obesity and adverse pregnancy and birth outcomes. Darker skin pigmentation and excess adiposity are risk factors for vitamin D inadequacy, which may further increase adverse perinatal outcomes. The current analysis explores the interactive effects of obesity and vitamin D inadequacy on birth outcomes among a sample of US Black women.

Methods: This was a secondary analysis of data from Environmental influences on Child Health Outcomes (ECHO) program. A subsample of 480 Black pregnant women participating in two ECHO cohorts (2006~2019) with circulating 25-hydroxyvitamin D (25(OH)D) assessed at 2^nd trimester of pregnancy were included. Participants were grouped based on vitamin D status [inadequate 25(OH)D ( < 50 nmol/L) and adequate (≥50 nmol/L)], and pre-pregnancy BMI [healthy weight (18.5-24.9 kg/m²), overweight (25.0-29.9 kg/m²), and obesity (≥30.0 kg/m²)]. A linear mixed model was used to examine the relationship between 25(OH)D and BMI groups both independently and as a statistical interaction on child birthweight and birth gestational age. Covariates included maternal age, season and gestational age of blood collection.

Results: Overall, the mean 25(OH)D concentration was 50.4 ± 21 nmol/L and 55% women were classified as inadequate. Among women with obesity, 62% had vitamin D inadequacy. There was no significant interaction effect of 25(OH)D and BMI group on birth outcomes, but independent effects were observed. Healthy weight as compared to obesity was associated with a statistically significant decrease in birth weight (ß=-268.1g, p=0.002) and gestational age at birth (ß=-0.652 wks, p=0.034). Vitamin D inadequacy, as compared to adequacy, was associated with a statistically significant decrease in birth weight (ß=-176.6g, p=0.026). In a subgroup analysis among the group with obesity, lower birthweight was observed in vitamin D inadequate vs. adequate group (birth weight 3,146 vs. 3,323 g, p=0.09).

Conclusions: The study showed a high prevalence of vitamin D inadequacy among US Black pregnant women, with a higher risk among those with obesity. Although there was no interaction effect, low vitamin D status may contribute to a lower birthweight. Further research is needed to confirm these findings and explore underlying mechanisms.

Funding Sources: N/A