Multivitamin supplementation has been associated with:

• Increased fertility and improvement in the female cycle
• Reduction in the incidence of morning sickness
• Reduction in congenital abnormalities (CA) other than NTDs, such as cleft palate
• Reduction in the risk of preterm delivery and subsequent low birth weight

Much of this work has come from the ongoing research of Czeizel¹. This Hungarian double blind randomised trial of a periconceptual multivitamin and mineral supplement, used a supplement containing 12 vitamins, 4 mineral and 3 trace elements. The placebo contained only the three trace elements.

Incidence of major congenital abnormalities (CA), such as NTDs, abnormality of the urinary tract and cardiovascular system, were halved in the Hungarian trial in those receiving multivitamin supplementation (20.6 compared to 40.6 per 1000 pregnancies). Similar reductions in CA have been confirmed by other studies using multivitamins^2,3,4.

The effect of B vitamins (other than folic acid) on the incidence of oro-facial clefts (OFC) has been investigated⁵. 206 mothers of infants with OFCs and 203 control mothers completed questionnaires at 14 months post partum. The results indicated that mothers of children with OFC had lower intakes of thiamin, niacin and pyridoxine.

The effect of vitamin supplementation on the incidence of low birth weight has been reviewed⁶. Compared to non users, supplement use in the first or second trimesters was associated with a four or two fold reduction respectively in risk of preterm delivery in a group of low income women. Risk of low birth weight was also reduced approximately two fold and risk of very low birth weight (<1500g) was reduced by 6-7 fold dependant on the period at which supplementation began.

The case for vitamin D supplementation has been well made especially in Asian women where sun exposure may be limited by clothing. In most studies supplementation with vitamin D improved neonatal handling of calcium but there was inconclusive evidence of benefits for foetal growth and bone development⁷. Supplementation at the levels routinely required to prevent vitamin deficiency (5-10mcg) seem to be adequate during pregnancy^7,8.

Pre-eclampsia

High blood pressure and the development of preeclampsia are the major causes of preterm birth and death in pregnant women and newborn babies. Nutrition interventions to prevent or ameliorate preeclampsia have been the subject of a number of Cochrane systematic reviews⁹.

From a review of 17 eligible studies (a total of 35,812 women and 37,353 pregnancies) where vitamins were commenced 20 weeks prior to conception and continued during pregnancy, the authors⁹ concluded that vitamin supplementation was associated with a reduction in pre-eclampsia risk compared to placebo.

In a second review of mineral supplementation¹⁰, later updated¹¹, researchers assessed the effects of randomised studies using calcium supplementation (1g or more) during pregnancy on hypertensive disorders of pregnancy and childbirth. There was a reduction in the incidence of high blood pressure in all studies. Risk reduction for both hypertension and pre-eclampsia was greater in those at high risk of developing hypertension and those with low calcium intakes.

A likely role for antioxidant vitamins in the prevention of pre-eclampsia has been proposed by a number of authors. It has been shown that circulating markers of oxidative stress are higher in pregnant women than in non-pregnant women^12,13. A study published in the Lancet¹⁴ indicated that supplementation with vitamin C and E together may be beneficial in the prevention of pre-eclampsia in women at increased risk.

Many women have inadequate intakes of magnesium and it has been suggested that magnesium might play a role in the prevention of pre-eclampsia. In a review of magnesium supplementation in pregnancy, Makrides¹⁵ was unable to find sufficient evidence of a positive effect. Of the 7 studies reviewed, only one was thought to be of high enough quality, and the poorer quality trials were judged to bias the result in favour of magnesium. More research needs to be carried out in this area.

In summary, multivitamin and mineral supplementation which augments an otherwise nutritionally inadequate diet has clearly been shown to have a significant impact on birth outcomes. Supplementation appears to reduce the incidence of congenital malformations such as NTD and those of the urinary tract, cardiovascular system and face. Nutritional research into pre-eclampsia, which affects approximately 10% of pregnancies, is encouraging. For women at known risk, supplementation with a broad spectrum vitamin and mineral supplement and encouragement to eat a healthy balanced diet seem prudent options.