Long term studies show that at least 450 mg of magnesium a day is needed to keep both pregnant mothers and their babies healthy.

Magnesium is a vital mineral for pregnant women because it can prevent premature birth, pregnancy induced high blood pressure (pre-eclampsia and eclampsia) and reduce pregnancy related constipation.

In a four month study of more than 550 pregnant women, those who took magnesium supplements had fewer premature babies. Additionally, fewer mothers were hospitalized before giving birth, and fewer newborn babies needed intensive care. Naturopath Tori Hudson, N.D., professor at the National College of Naturopathic Medicine in Portland, Oregon, says that the best time for pregnant women to increase their magnesium is during their first trimester if they want to prevent low birth rate in their babies.

Many women now take extra magnesium to prevent constipation during pregnancy. Gynecologist Uzzi Reiss, M.D., has told some of his patients they could take magnesium to bowel tolerance during their pregnancies to avoid the pressure related constipation. Some of his patients took as much as 1,000 mg of supplementary magnesium a day in addition to whatever amounts they got from their diets. Before increasing magnesium, pregnant women should always check with their doctors. Nan Kathryn Fuchs, Ph.D. - author of User's Guide to Calcium & Magnesium.

Although magnesium is the treatment of choice for pregnancy-induced high blood pressure, it could be used more widely. Many researchers suggest that pregnant women routinely take magnesium throughout pregnancy to prevent complications during delivery and postpartum, and to help prevent premature births.(Almonte RA et al., Gestational magnesium deficiency is deleterious to fetal outcome. Biol Neonate, vol 76, no.1, pp. 26-32, 1998.)

Clinical trials have demonstrated that mothers supplementing with magnesium have larger, healthier babies and lower rates of pre-eclampsia, premature labor, sudden infant death, and birth defects, including cerebral palsy. (Seelig MS Toxemias of pregnancy, postpartum cardiomyopathy and SIDS in consequences of magnesium deficiency in the enhancement of stress reactions; preventive and therapeutic implications: a review,  J Am Coll Nutr, vol 13, no. 5, pp. 429-446, 1994.)