The interplay between magnesium and hypertensive disorders of pregnancy in a pregnant, Black South African population.

Abstract

Background South Africa, a low- to middle-income country, faces a high burden of maternal and neonatal morbidity and mortality, with hypertensive disorders of pregnancy— particularly preeclampsia—contributing substantially to these outcomes. Magnesium plays a critical role in vascular regulation, endothelial function, and blood pressure control. Although magnesium sulphate is well established in the management of severe pre-eclampsia, the relationship between circulating maternal magnesium levels and the development of pre-eclampsia remains poorly understood, especially in populations with high rates of obesity and HIV. Aim To investigate the association between maternal serum magnesium concentrations and preeclampsia, and to examine the influence of HIV status and obesity on this relationship in a South African antenatal population. Methods This cross-sectional study included 252 pregnant Black South African women, categorised into: First Visit Normotensive (First VisitNT), Term Normotensive (TermNT), early-onset preeclampsia (EOPE), and late-onset pre-eclampsia (LOPE). Serum magnesium was measured using atomic absorption spectrophotometry. Differences between groups were assessed using analysis of variance (ANOVA) with Bonferroni post-hoc tests, while associations with preeclampsia were examined using chi-square tests and multinomial logistic regression, adjusting for body mass index, HIV status, and gestational age. Results Among normotensive women, serum magnesium levels declined significantly from the first antenatal visit to term (0.78 ± 0.08 mmol/L vs. 0.72 ± 0.10 mmol/L; p < 0.001). This decline was not observed in women with pre-eclampsia, whose magnesium levels remained stable or slightly elevated. Hypomagnesaemia (<0.66 mmol/L) was most prevalent in the TermNT group (23.9%) and was associated with lower odds of pre-eclampsia (odds ratio [OR] = 0.216, 95% confidence interval [CI]: 0.065–0.721, p = 0.013). Obesity was a strong predictor of both early-onset pre-eclampsia and late-onset pre-eclampsia, whereas HIV status showed no significant association with magnesium levels or pre-eclampsia risk. Conclusion In this cohort, normotensive pregnancies showed a physiological decline in serum magnesium, a pattern absent in pre-eclampsia. The inverse association between hypomagnesaemia and preeclampsia suggests altered magnesium regulation in hypertensive pregnancies rather than a protective effect of low magnesium. These findings highlight the complexity of magnesium’s role in pre-eclampsia pathophysiology and underscores the need for longitudinal studies to clarify causality and inform targeted antenatal interventions.