Background: The effect of maternal vitamin D status on the birth weight of offspring is controversial as the results are inconsistent between different populations. This large retrospective cohort study aimed to assess the relationship between maternal vitamin D levels and birth weight of neonate.
Methods: Serum samples were collected from 10,586 Chinese women in the 2 nd trimester of pregnancy, and the 25-hydroxyvitamin D [25(OH)D] level of the participants was assessed. Using the INTERGROWTH-21st standards, the offsprings were classified into three groups based on their gestational age and birth weight, which were as follows: small for gestational age (SGA), appropriate for gestational age (AGA), and large for gestational age (LGA).
Results: The average maternal vitamin D concentration was 61.1 nmol/L. The 25(OH)D concentrations were <75.0, <50.0, and <25.0 nmol/L in 76.6%, 31.1%, and 1.6% of the participants, respectively. Approximately 6.4%, 86.4%, and 7.2% of women delivered SGA, AGA, and LGA infants, respectively. No significant differences were observed in vitamin D levels between the three groups (P = 0.562). With the increase in 25(OH)D levels, the risk of SGA and LGA tended to increase and decrease, respectively. However, the results were not precise. AGA was not affected by 25(OH)D levels. The results of the curve fitting and threshold effect analyses did not support the correlation between vitamin D levels and SGA or LGA. Based on the univariate prediction model and the model that adjusted for the risk factors, the area under the curve was extremely small. Thus, 25(OH)D level is not an effective predictor of SGA and LGA.
Conclusions: Low maternal vitamin D levels were not associated with SGA or LGA.