Post Hoc Analysis of National Institute of Child Health and Human Development Vitamin-D Pregnancy Cohort and The Role of Functional Vitamin-D Deficiency in Pregnancy

Abstract

Objective: Conduct a secondary, post-hoc analysis of NICHD vitamin D (vitD) pregnancy study by Hollis et al. (Hollis, 2011), which reported on the effect of vitD supplementation in pregnant women; and determine the potential interaction between intact parathyroid hormone (iPTH) concentrations, vitD status, and various comorbidities associated with pregnancy. Hypothesis: Women with low 25(OH)D concentrations and high iPTH concentrations during pregnancy, known as functional vitD deficiency (FVDD), were more likely to acquire complications also affecting their neonates. Study Design: This post-hoc analysis of data collected from a diverse group of pregnant women participating in the NICHD vitD pregnancy study, was applied to investigate the applicability of the concept of FVDD in pregnancy (Hemmingway, 2018) in identifying potential risks for certain comorbidities of pregnancy. This analysis defines FVDD as maternal serum 25(OH)D concentrations below 20 ng/mL and iPTH concentrations above 65 pg/mL creating a definitive ratio number, 0.308, to classify mothers as having FVDD prior to delivery (PTD). Statistical analyses were performed using SAS 9.4 (Cary, NC). Results: 281 women (85 African American, 115 Hispanic, 81 Caucasian) with 25(OH)D and iPTH concentrations measured at monthly visits were included in this analysis. No statistically significant association was found between mothers classified as having FVDD at baseline or one-month PTD and hypertensive disorders of pregnancy, infection, or admittance to the NICU. When combining all comorbidities of pregnancy in this cohort, results showed those with FVDD at baseline, 24 weeks’ gestation, and one-month PTD were more likely to experience a comorbidity (p=0.001; p=0.001; p=0.004, respectively). Those with FVDD one-month PTD were 7.1 times (CI 1.71-29.81) more likely to have preterm birth (<37 weeks) than women without FVDD. Conclusions: Participants were more likely to have experienced preterm birth if they met the criteria for FVDD. This study supports the importance of FVDD during pregnancy.