Magnesium And Calcium Supplementation During Pregnancy – New Research

Two new studies to be published in BJOG: An International Journal of Obstetrics and Gynaecology in August 2007 look at mineral supplementation and the prevention of specific conditions during pregnancy.

In the first study, researchers examined the effect of magnesium supplementation and the development of hypoxic-ischaemic encephalopathy (HIE) in babies. HIE is the reduction of oxygen supply to tissues and the brain due to inadequate blood flow. The indications of HIE or perinatal hypoxia are: decelerated fetal heart rate, low Apgar Scores, meconium aspiration pneumonia(meconium stained full-term infants with signs of respiratory distress from birth) and stillbirths at term. These outcomes are often linked to poorly nourished mothers who lack magnesium in their diet during pregnancy.

4494 women attending antenatal clinics at a midwife obstetric unit and two hospitals in Cape Town, South Africa were recruited for the study. They received either a magnesium supplement (128 mg elemental magnesium) or a placebo daily over a period of four weeks.

Findings show that magnesium supplementation had no effect on the course of the pregnancy or fetal development but some benefits were detected on the fetus during labour. Perinatal hypoxia during birth was less in the women who took the magnesium supplements when pregnant. This suggests improved perinatal outcomes were the result of regular, controlled magnesium intake for pregnant women who were deficient in magnesium.

Dr Vincent Harrison from the Department of Neonatal Medicine at the University of Cape Town said “This study was designed primarily to determine the effect of magnesium supplementation on the incidence of neonatal encephalopathy (HIE). Overall, women with inadequate stores of magnesium were seven times more likely to deliver an infant with HIE than those with normal levels of the cation.”

“Additional magnesium appeared to benefit the fetus during labour. Significantly fewer showed fetal heart rate irregularities, meconium-stained liquor and partogram abnormalities. The supplemented group also had fewer late stillbirths either before or during labour.”

“It must be stressed that these secondary findings, although of interest, need to be substantiated by further work. Until then, supplementation cannot be recommended but poorly nourished women should be encouraged to eat a diet that contains adequate magnesium, in particular brown – rather than white – bread.”

In the second study, a group comprising South African, English and Brazilian researchers examined existing studies into whether calcium supplementation is responsible for lowering the incidence of pre-clampsia in pregnancy.

The prevalence of pre-eclampsia in women from societies with a calcium-rich diet has been observed to be low. Researchers hypothesised that regular calcium intake could help prevent hypocalcaemia (low blood calcium) and pre-eclampsia, along with its outcomes including preterm labour.

12 good quality international studies which looked at evidence from 15, 528 women were reviewed. Researchers found from the findings that there is less high blood pressure associated with women who had calcium supplements. Supplementation halves the risk of developing pre-eclampsia during pregnancy. Women with low calcium intake and were considered as high risk before the trials experienced a reduction in gestational hypertension (high blood pressure measured after 20 weeks) after taking calcium supplements when pregnant. Researchers noted that no adverse effects of calcium supplementation were recorded in the trials reviewed. There was no conclusive evidence of the benefits of calcium supplementation in women that had adequate dietary intake of calcium. The authors believe that further research is required to provide reassurance to the public and medical professionals that there are no adverse effects of calcium supplementation.

Dr Justus Hofmeyr, Head of the Department of Obstetrics and Gynaecology at East London Hospital in South Africa, who led the study said “Previous reports have shown that women with low calcium diets are at increased risk of developing high blood pressure during pregnancy. Our systematic review found that giving calcium supplements in the second half of pregnancy reduced the rate of high blood pressure, but not of protein in the urine (the other hallmark of pre-eclampsia).”

“In our commentary, we recommend further research to find out whether improving calcium intake from before pregnancy might reduce not only blood pressure, but associated problems such as protein in the urine as well. We suggest that fortification of staple foods might make the benefits of adequate calcium intake available to all pregnant women, not only those with access to antenatal care.”

Professor Philip Steer, BJOG editor-in-chief said, “While these studies show that the consumption of certain minerals during pregnancy results in favourable outcomes for mother or baby, it must be stressed that in these studies, the intake of supplements are carefully measured.”

“Women should attend their antenatal clinics so that tests identifying problems can be carried out. If they are interested to know more about supplementation, they should speak to their GPs and midwives for further advice.”

“We should note that women who do not have a deficiency in magnesium or calcium need to be careful about taking extra supplements if they don’t need it.”


GJ Hofmeyr, L Duley, A Atallah Dietary calcium supplementation for prevention of pre-eclampsia and related problems: a systematic review and commentary BJOG: (OnlineEarly Articles). doi:10.1111/j.1471-0528.2007.01389.x

Harrison, S Fawcus, E Jordaan Magnesium supplementation and perinatal hypoxia: outcome of a parallel group randomised trial in pregnancy BJOG (OnlineEarly Articles). doi:10.1111/j.1471-0528.2007.01409.x