Cord serum vitamin D in a South China birth cohort.

Vitamin D deficiency during pregnancy has been associated with many adverse pregnancy and birth outcomes. Low serum 25-hydroxyvitamin D (25OHD) levels (<30 nmol/L) increases the risk of nutritional rickets. This study aimed to investigate the concentration of cord serum 25OHD in a birth cohort in Guangzhou, China and determine whether maternal lifestyle factors had any effect on these levels.A total of 854 pregnant women giving birth between Dec 2016 and Dec 2017 were recruited to this study. Basic information was obtained from the clinical database. A voluntary retrospective pregnancy lifestyle questionnaire was completed by 388 participants. The concentration of serum 25OHD, calcium, phosphorus, and alkaline phosphatase (ALP) were measured in umbilical cord blood.The mean (SD) of cord serum 25OHD was 44.7 (16.7) nmol/L. The prevalence of cord 25OHD <30 nmol/L was 22.2% and 70.4% had levels <50 nmol/L. The prevalence of vitamin D deficiency is higher in infants born in winter months (31% <30 nmol/L and 76% <50 nmol/L), compared to those born in the summer (12% <30 nmol/L and 64% <50 nmol/L). Infants born to women taking a vitamin D containing supplement had approximately 10 nmol/L higher levels of 25OHD than those who did not supplement their diets.Summer born infants have higher serum 25OHD levels at birth, but there are still infants being born with vitamin D deficiency. Vitamin D containing supplement use during pregnancy was effective in raising cord serum vitamin D levels.