Magnesium supplementation during pregnancy: a double-blind randomized controlled clinical trial.

Four hundred young normotensive primigravid women between 13 and 24 weeks' gestation were randomly allocated to one of two study groups. One group received placebo tablets and the other group received 365 mg of elemental magnesium daily (as magnesium aspartate hydrochloride). Three hundred seventy-four patients completed the study, 189 in the placebo group and 185 in the treatment group. There were no significant differences between the two groups regarding serum calcium, uric acid, or electrolyte levels. However, the magnesium-supplemented group had significantly higher magnesium levels at delivery (1.68 +/- 0.03 mg/dl vs. 1.56 +/- 0.03 mg/dl, p less than 0.01). There were no significant differences in either systolic or diastolic blood pressures between both groups either at time of enrollment or at subsequent gestational ages later during pregnancy. Analysis of variance for repeated measurements and Fisher's least significant difference testing indicated a significant increase (p less than 0.01) in blood pressure from the level at the time of enrollment to the level achieved at or beyond 37 weeks' gestation in each group. There were no significant differences between the two groups regarding any of the following parameters: incidences of preeclampsia, fetal growth retardation, preterm labor, birth weight, gestational age at delivery, or number of infants admitted to the special care unit. Magnesium supplementation during pregnancy did not improve pregnancy outcome in our population.