Is it safe to take magnesium during pregnancy?

Pregnancy has its own recommended amount, and the same upper limit as for other adults. The US recommended amount in pregnancy is 350 to 400 mg a day from food and supplements together. The upper limit from supplements is 350 mg a day, the same as for other adults.^[1] EFSA, the EU food safety authority, found no evidence that pregnancy raises the need, and sets 300 mg a day.^[2]

A 2014 Cochrane review of 10 trials with 9,090 women found no clear effect of magnesium supplements on stillbirths and newborn deaths, small babies or pre-eclampsia. Only 2 of the trials were of high quality.^[3] One analysis showed more newborn deaths with magnesium. This came mostly from one trial, and the difference went away when deaths from severe birth defects were left out.^[3] A 2022 review of 7 trials found a lower risk of pre-eclampsia (risk ratio 0.76), but not in women at normal risk.^[4]

For leg cramps in pregnancy, trial results conflict.^[5]

Magnesium sulphate given by doctors for pre-eclampsia is a different, medical use. In 10,141 women it lowered the risk of eclampsia by 58%.^[6]

Pregnant women should ask a doctor or pharmacist before taking more than 350 mg a day from supplements.^[1]