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Journal Summary: Vitamin D Supplementation in Pregnancy and Lactation and Infant Growth

Vitamin D supplementation in pregnancy does not improve birthweight or infant growth at 12 months among women with high levels of Vitamin D deficiency.

E. Roth, S.K. Morris, S. Zlotkin et al. Vitamin D Supplementation in Pregnancy and Lactation and Infant Growth. N Engl J Med 2018;379:535-46.

Summary

While Vitamin D deficiency has been implicated in many adverse outcomes involving pregnancy and infant growth, most of these studies have been cohort studies, with relatively few randomised studies. 

In this study, 1300 Bangladesh women with high levels of Vitamin D deficiency were randomised to one of 5 groups in pregnancy; (i) no Vitamin D supplementation; (ii) 4200 IU Vit D/ week; (iii) 16,800 IU Vit D/ week; (iv) 28,000 IU Vit D/ week and (v) 28,100 IU Vit D/ week plus a further 28,100 IU/ week for 26 weeks after delivery. The baseline levels of Vitamin D in all groups were comparable (around 27 nmol/ L across all groups). There was good compliance and good follow up of nearly 90% of infants at 1 year of age. 

The main finding of this study was that Vitamin D supplementation did not improve birthweight (average ~2.7kg), the rate of small for gestational age (~45% for all groups) or postnatal growth. The prevalence of stunting (length for age z score of -2) ranged from 13-19%, with no difference seen across the treatment groups. There were no beneficial (or harmful) effects on gestational hypertension, duration of gestation or preterm birth. Of note, there were 4 cases of rickets; 3 in the placebo group and 1 in the lowest supplementation group. In this group the daily supplementation dose (equivalent 600 IU/day) was lower than we would generally be recommend for women with severe deficiency (<30nmol/l). 

Overall, this study demonstrated that Vitamin D is safe to take, with no adverse maternal or infant events related to hypercalcemia in any group.  

Clinical implications

This study reports that supplementation of women with Vitamin D deficiency does not improve obstetric, perinatal or infant growth outcomes, although was underpowered for the uncommon, but important outcome, of nutritional rickets. This study supports there is no case for routine screening for Vitamin D in low risk women. Vitamin D levels even in this highly deficient population were mostly corrected with the lowest dose of supplementation- similar to that provided by routine prenatal vitamins. This suggests routine pregnancy supplements would correct for minor degrees of Vitamin D deficiency related to seasonal variation etc. High risk women (for example those who are veiled, dark skinned or obese) should be screened to ensure that rare cases of severe deficiency are diagnosed and treated with increased Vitamin D supplementation to avoid the small risk of infant rickets. 

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