Objectives To determine the prevalence of vitamin D deficiency in pregnant women and their neonates and to examine factors associated with vitamin D deficiency.
Design and patients Population-based study of pregnant women and their neonates from South-eastern Sydney, Australia.
Measurements Serum 25 hydroxy-vitamin D (25-OHD), PTH, calcium, albumin, phosphate and alkaline phosphatase were measured in women at 23–32 weeks gestation and on cord blood at delivery. Maternal skin phototype was recorded using the Fitzpatrick scale.
Results Vitamin D deficiency (defined as 25-OHD ≤ 25 nmol/l) was found in 144 of 971 (15%) women and 98 of 901 (11%) neonates. Median 25-OHD was 52 nmol/l (range 17–174) in mothers and 60 nmol/l (17–245) in neonates. Maternal 25-OHD levels varied by season, with lowest levels in late winter/early spring (P < 0·001). Factors associated with maternal vitamin D deficiency in multiple logistic regression were (OR, 95% CI): maternal birthplace outside Australia: 2·2 (1·4–3·5, P = 0·001), dark skin phototype: 2·7 (1·6–4·5, P < 0·001), wearing a veil: 21·7 (11·7–40·3, P < 0·001) and younger maternal age: 0·93 (0·89–0·97, P = 0·001). Maternal vitamin D deficiency increased the risk of neonatal vitamin D deficiency (OR 17·2, 95% CI 8·8–34·3) and birth weight was lower among infants of deficient vs. sufficient mothers: mean (SD) 3245 g (545) vs. 3453 g (555), P < 0·001.
Conclusions Vitamin D deficiency is common among pregnant women; immigrant, veiled and dark skinned women are at greatest risk. Maternal vitamin D deficiency increases the risk of neonatal vitamin D deficiency and lower birth weight.