Magnesium supplementation and perinatal hypoxia: outcome of a parallel group randomised trial in pregnancy

Objective To determine the effects of magnesium supplementation in pregnancy on the incidence of hypoxic-ischaemic encephalopathy (HIE). Design A randomised double-blind placebo-controlled study. Setting A Midwife Obstetric Unit and its two referral hospitals in Cape Town, South Africa. Population A group of 4494 black pregnant women of low socio-economic status. Method Mothers, from the time of booking until delivery, were randomised to receive two identical tablets daily, containing either 128 mg slow-release magnesium stearate or lactose sugar. Main outcome measures Primary: The incidence of HIE. Secondary: The incidence of fetal heart rate decelerations, term Stillbirths, Low Apgar Scores, Meconium Aspiration Pneumonia. Results The incidence of HIE (0.9%) was considerably less than anticipated (2%). There were 22 infants in the placebo group and 15 infants in the supplemented group (P = 0.279). The difference was not significant. Secondary outcomes such as late fetal heart rate decelerations (P = 0.002) and term stillbirths (P = 0.016) were reduced significantly in the supplemented group, but this finding needs further substantiation. Conclusions Magnesium supplementation did not reduce the incidence of HIE significantly, probably because the study was underpowered and compliance was relatively poor.