Dietary modification, vitamin/mineral supplementation, and treatments during pregnancy - technical
In the United Kingdom and the United States of America spina bifida or anencephaly (neural tube defects) affect about 1 in 1000 pregnancies. The neural tube develops and then closes within 28 days of conception. Women who take 400 µg folic acid daily around the time of conception and for the first 2 months of pregnancy reduce their risk of a pregnancy complicated by neural tube defects by approximately 70%. In some countries the fortification of food with folic acid provides an extra 100 µg/day of folic acid, which appears to be effective in lowering rates of neural tube defects. Women who have had a baby affected by spina bifida are advised to take a higher dose of folic acid (5 mg/day).
Multivitamins and other supplements
Multivitamin preparations without folic acid do not reduce the risk of neural tube defects. Multivitamins taken periconceptually may reduce the risk of some congenital heart defects, but beyond the first trimester are of no proven benefit for healthy women on a balanced diet. Antioxidant vitamins (vitamin C 1000 mg and vitamin E 400 IU daily) taken from mid pregnancy do not reduce the incidence of pre-eclampsia and even increase the incidence of low birth weight babies.
Women should keep up adequate stores of vitamin D during pregnancy and when breast feeding. Women at high risk of vitamin D deficiency should be particularly encouraged to take supplemental vitamin D (10 µg/day).
Certain liver products and vitamin A supplementation above 700 µg daily increase the risk of embryonic teratogenesis and should be avoided. In the developing world where diet is poor, vitamin A supplements and zinc improve fetal outcome. See for further discussion.
In the developed world, supplemental iron should be reserved for those who have a haemoglobin of less than 9.5 g/dl and a mean corpuscular volume of less than 84 fl in the third trimester. In the developing world, malnutrition and chronic infection diminish iron stores that are further exhausted during pregnancy. Under these conditions, routine supplemental iron and folate improves maternal and neonatal outcome. See Chapter 14.2 for further discussion.
Sea food, fish oils, and omega-3 fatty acids
There is conflicting information regarding the harm and benefit that may follow ingestion of seafood and its unsaturated fatty acids during pregnancy. Official guidance from United States federal agencies recommends that seafood intake should be limited to less than 340 g per week during pregnancy because of the fear of methylmercury ingestion. This consequence has not eventuated from the ingestion of fish outside Japan, indeed children born to mothers who eat less than 340 g seafood during pregnancy have a greater risk of being in the lowest quartile for verbal IQ and other scores for poor social development. As a consequence of this latter observation many women take omega-3 fatty acids to improve their child’s intelligence, but whether this is an advisable strategy has yet to be proven. For example, cod liver oil, which contains high doses of long-chain polyunsaturated fatty acids, is associated with an increased odds ratio of pre-eclampsia and gestational hypertension.
Prophylaxis against pre-eclampsia
Pre-eclampsia is discussed in . At present, prophylactic measures to prevent the condition have proved only weakly beneficial or even harmful, e.g multivitamins. Low dose aspirin 60 to 150 mg daily, given to women at increased risk of pre-eclampsia, reduces the incidence by 17%. Calcium supplementation is beneficial to populations of women with a low dietary intake of calcium. However, our ability to prevent or treat this condition will remain inadequate until our understanding of its pathophysiology improves.
Iodine and thyroxine
Neurodevelopment of the fetus during the first trimester depends on thyroxine and maternal subclinical hypothyroidism has been associated with impaired neurodevelopment in the infant. It has therefore been suggested that all women should be screened for hypothyroidism before conception or in early pregnancy, but more easily applied public health measures to increase iodine intake are generally more practical, and the benefit of thyroxine replacement in women with ‘low normal’ thyroxine levels is not proven.