Maternal 25-hydroxyvitamin D and parathyroid hormone concentrations and offspring birth size

Context: There is inconsistent evidence that maternal 25-hydroxyvitamin D [25-(OH)D] deficiency may impair fetal growth. Objective: The objective of the study was to examine the relationship between maternal 25-(OH) D and PTH concentrations at less than 16 and 28 wk gestation and offspring birth size. Design: This was an observational study. Setting: The study was set at a hospital antenatal clinic. Participants: Women with singleton pregnancies, before 16 wk gestation, participated. Interventions: No interventions were used. Main Outcome Measure: Knee-heel length at birth was the main outcome measure. Results: Altogether 374 of 475 (79%) women completed this study. We found no evident relationship between birth size measures and maternal 25-( OH) D or PTH at recruitment (similar to 11 wk). Gestation length was 0.7 wk (95% confidence interval -1.3, -0.1) shorter and knee-heel length was 4.3 mm smaller (-7.3, -1.3) in infants of 27 mothers with low 25-(OH) D (<28 nmol/liter) at 28-32 wk vs. babies whose mothers had higher concentrations. This latter difference was reduced to -2.7 mm (-5.4, -0.1) after adjustment for gestation length, suggesting some of the apparent growth deficit is explained by shorter gestation. There was no evidence that other birth measures were affected. Maternal PTH concentration at 28-32 wk was positively related to knee-heel length, birth weight, and mid-upper arm and calf circumferences. These associations were independent of 25(OH) D concentration. Conclusions: Low maternal 25-(OH) D in late pregnancy is associated with reduced intrauterine long bone growth and slightly shorter gestation. The long-term consequences for linear growth and health require follow-up. The positive relationship between maternal PTH and measures of infant size may relate to increased mineral demands by larger babies, but warrants further investigation.