The association between serum magnesium levels and hypertensive disorders of pregnancy.

Background:  Evidence on circulating magnesium and hypertensive disorders of pregnancy in African populations is limited. We assessed between-group differences in serum magnesium and examined associations with early-onset pre-eclampsia and late-onset pre-eclampsia.

Methods:  We conducted an analytic cross-sectional study of 252 pregnant women sampled as four clinical groups: normotensive at a first antenatal visit, normotensive at term, early-onset pre-eclampsia, and late-onset pre-eclampsia. Serum magnesium was measured. Between-group differences were tested using one-way analysis of variance with contrasts. Associations with early-onset or late-onset pre-eclampsia versus normotensive groups were estimated using logistic regression adjusted for gestational age, body mass index, and human immunodeficiency virus status. We report effect sizes and 95 percent confidence intervals.

Results:  Serum magnesium was lower in normotensive women at term compared with those sampled at the first antenatal visit, consistent with physiological change across gestation. No comparable decrease was observed in early-onset or late-onset pre-eclampsia. The prevalence of hypomagnesaemia differed by group and was lowest at the first antenatal visit among normotensive women, while pre-eclampsia groups showed a divergent pattern. In adjusted models, obesity was positively associated with early-onset and late-onset pre-eclampsia, whereas human immunodeficiency virus status showed no significant association.

Conclusions:  In this South African cohort, cross-sectional comparisons demonstrate lower serum magnesium at term in normotensive pregnancies and a divergent profile in pre-eclampsia, supporting the hypothesis of altered magnesium regulation in hypertensive disorders of pregnancy. Results represent associations rather than causal effects and motivate future longitudinal research with repeated and intracellular magnesium measurements to clarify temporality and clinical relevance.Contribution: This article adds to the limited literature on Mg dynamics in pregnancy and highlights the need for population-specific strategies to reduce maternal mortality.