What this study adds
obesity, nerve injury, jaundice, psychological distress, PPH, bone mass, trauma
OBESITY, INTRACRANIAL HAEMORRHAGE, VITAMIN D DEFICIENCY, INFANT MORBIDITY
Supplementation with 1000 IU/day cholecalciferol did result in a difference in mode of delivery. The proportion of women having a SVD in those randomized to cholecalciferol was higher than the placebo group with fewer instrumental deliveries but no difference in Caesarean section. As instrumental delivery is associated with increased risk of perineal trauma, maternal psychological distress and infant morbidity (for example trauma, jaundice, facial nerve injury, intracranial haemorrhage), vitamin D supplementation might reduce these outcomes, although we were not able to assess this directly. Corcoy The mechanism by which vitamin D might increase SVD rates could result from effects on uterine contractility and muscle strength. The vitamin D receptor (VDR) has been isolated in human myometrium,The observed reduction in PPH by cholecalciferol likely reflects the difference in delivery mode. PPH risk is higher in instrumental and operative deliveries,As these are hypothesis-generating post hoc analyses, and the reasons for operative delivery were not documented, future trials would need to focus on delivery characteristics, such as labour timings, use and reasons for any intervention and analgesia, both to confirm our findings and attempt to elucidate the underlying mechanisms. Future studies should additionally aim to establish the benefits of vitamin D supplementation on these outcomes in specific risk groups for both vitamin D deficiency (for example, obesity, prolonged hospital admission or Black, Asian and Minority Ethnic groups) and adverse obstetric outcomes, and with randomization stratified by factors associated with the biochemical response to vitamin D supplementationBased on our findings, the number of women needed to treat with 1000 IU/day cholecalciferol to prevent one instrumental delivery is 14. As 1000 IU/day cholecalciferol for the duration of pregnancy for one woman in the UK costs ∼£15 (NHS prescribing cost of £1.45 for 30 tablets, British National Formulary 2021), the cost to prevent one instrumental delivery would be ∼£210. This, however, would be offset against the reduction in maternal and neonatal morbidity, and thus could be a relatively cheap intervention and warrants further investigation. If these findings and the other identified benefits of higher dose antenatal vitamin D supplementation such as increased offspring bone mass