A healthy balanced diet should largely obviate the need for vitamin and mineral supplementation; however, pregnancy and lactation create extra nutritional demands that may make supplementation advisable.
Folic acid deficiency is associated with megaloblastic anaemia and birth defects (especially neural tube defects). All women should take preconceptual folic acid (500 micrograms [0.5 mg] folate daily) while attempting pregnancy to reduce the risk of neural tube defects. As 50 per cent of pregnancies are unplanned, when contraception is not being used, a dose of 500 micrograms daily should be taken.
Vitamin B12 is essential for infant neurodevelopment. Undiagnosed maternal vitamin B12 deficiency may result in irreversible neurological damage to the breastfed infant. Although maternal vitamin B12 deficiency is uncommon, the majority of women with deficient B12 levels are asymptomatic.
Studies have found that vitamin B6 reduces the severity of nausea but not vomiting in the first trimester. Vitamin B6 was also associated with a decrease in the risk of dental decay in pregnant women.
Studies of pregnant women in Australia and New Zealand have found a disturbing frequency of vitamin D deficiency. Women at increased risk include those with reduced sunlight skin exposure. Vitamin D deficiency is known to be an important risk factor for the development of osteoporosis in later life.
Vitamin K is a fat soluble vitamin crucial to the production of many proteins involved in the coagulation process. Vitamin K may be administered in late pregnancy to women with proven cholestasis of pregnancy, due to reduced vitamin K absorption. Vitamin K supplements have also been suggested for women at risk of having low levels in the first trimester e.g. on liver enzyme-inducing antiepileptics.
The iron demands of pregnancy are particularly pronounced due to the expanded red cell volume, blood loss around the time of delivery and the demands of the developing fetus and placenta. Iron supplementation will generally be recommended for women at particular risk of iron deficiency. This includes vegetarians and women with a multiple pregnancy.
All women should have their haemoglobin level checked at the first antenatal visit and again at approximately 28 weeks’ gestation and any anaemia investigated and treated. Routine iron supplementation is not recommended in every pregnancy.
Providing there is no vitamin D deficiency, a balanced diet will have sufficient calcium for pregnancy and lactation. If the woman avoids dairy in her usual diet, and does not consume alternative high calcium food (e.g. calcium enriched soya milk), calcium supplementation is advisable (RDI 1200 mg/day).
A systematic review found calcium supplementation almost halved the risk of pre-eclampsia, reduced the risk of preterm birth and occurrence of the composite outcome ‘death or serious morbidity’. The effect was greatest for women with low baseline calcium intake.
Iodine plays a critical role in neuropsychological development of the fetus throughout gestation and in the first two years of life. The National Iodine Nutrition Survey (2006) has identified that the Australian population is mildly iodine deficient. Iodine uptake by the thyroid is higher in pregnancy and the iodine reserve in the thyroid can decrease to approximately 40 per cent of preconception levels.
The National Health and Medical Resarch Council (NHMRC) recommends that all women who are pregnant, breastfeeding or considering pregnancy, take an iodine supplement of 150 micrograms each day (NHMRC 2010). Information from the SA Perinatal Practice Guideline: vitamin and mineral supplementation in pregnancy.
Other vitamin supplementation
There is little evidence to support routine supplementation of high-dose fat soluble vitamins A and E, and excessive quantities of fat soluble vitamins may be harmful. Vitamin A supplementation (intake above 10,000 units of Retinol) may cause birth defects and should be avoided. Pregnant women should be informed that liver and liver products may contain high levels of vitamin A, and therefore consumption of these products should also be avoided. Betacarotene, the vegetable form of vitamin A is not associated with an increased rate of birth defects.