Vitamin D levels during pregnancy and associations with birth weight and body composition of the newborn: a longitudinal multiethnic population-based study

We investigated associations between serum 25-hydroxyvitamin D )25)OH) D) in pregnancy and birth weight and other neonatal anthropometric measures. The present study was a population-based, multiethnic cohort study of 719 pregnant women )59% ethnic minorities) in Oslo, Norway, delivering a singleton neonate at term and with birth weight measurements. In a representative sample, anthropometric measurements were taken. Maternal 25)OH) D was measured at gestational weeks 15 and 28. Women with 25)OH) D <37nmol/l were recommended vitamin D-3 supplementation. Separate linear regression analyses were performed to model the associations between 25)OH) D and each of the outcomes: birth weight, crown-heel length, head circumference, abdominal circumference, sum of skinfolds, mid-upper arm circumference and ponderal index. In early pregnancy, 51% of the women were vitamin D deficient )25)OH) D<50nmol/l). In univariate analyses and in models adjusting for maternal age, parity, education, prepregnancy BMI, season, gestational age and neonate sex, maternal 25)OH) D was significantly associated with birth weight, head circumference, abdominal circumference and ponderal index )P<0.05 for all), when used as a continuous variable and categorised )consistently low, consistently high, increasing and decreasing level). However, after adjusting for ethnicity, 25)OH) D was no longer associated with any of the outcomes. Sex-specific associations for abdominal circumference and sum of skinfolds were found )P-for (interaction)< 0 . 05). In conclusion, in a multiethnic cohort of pregnant women with high prevalence of vitamin D deficiency, we found no independent relation between maternal vitamin D levels and any of the neonatal anthropometric measures, and the strong association between ethnicity and neonatal outcomes was not affected by maternal vitamin D status.