Low-normal serum selenium early in human pregnancy predicts lower birth weight

There are limited data to support the recommended daily allowance of 60 μg/d for dietary selenium for pregnant women. In addition, low dietary selenium may exacerbate iodine deficiency and influence thyroid function. The objective was to study relationships among selenium nutrition, thyroid function, and pregnancy outcomes. We conducted a case-control study nested within a cohort of young, healthy women participating in the Camden (NJ) Study, a 20-year ongoing investigation of effects of maternal nutrition on pregnancy outcomes. Cases were 107 women who delivered preterm, and controls were 126 women who delivered full-term neonates. The mean gestational age at blood collection was 15.6 ± 0.6 weeks (mean ± SE). Diet selenium intake was 103 ± 5 μg/d. Serum selenium concentrations were higher in cigarette smokers but were not significantly associated with preterm delivery or serum thyroid stimulating hormone concentration. Neonates born to mothers in the lowest decile of serum selenium (decile median, 8.57 μg/dL or 1.09 μmol/L) had significantly lower birth weights (β = -259 ± 100 g) compared with those in the 9 highest deciles. For the subgroups of full-term and preterm neonates, maternal serum selenium and birth weight were significantly associated only for the full-term deliveries. For full-term pregnancies, low-normal serum selenium in the first or second trimester predicts lower birth weight, but prematurity masks this relationship. The effects of selenium do not appear to be mediated by its influence on thyroid function during pregnancy. If the association that we found is causal, maternal selenium nutrition may have a substantial effect on birth weight.