Maternal deficiency of certain nutrients has been linked to a number of negative health consequences for mother and child.
Risks include restricted fetal growth, low birth weight, skeletal deformities, and pre-eclampsia.
These well-known dangers support a huge vitamin, mineral, and micronutrient industry aimed at pregnant women.
Typically, these tablets will contain 20 or more vitamins and minerals, often including a range of B vitamins, C, D, E, K, iodine, folic acid, magnesium, zinc, selenium, and copper.
The supplements normally cost around £15 (roughly $19) per month.
A new report, published in the Drug and Therapeutics Bulletin, assessed the existing literature to investigate whether these products translate into better outcomes for women and their children.
Which supplements really matter?
Although studies have been done on the effectiveness of certain supplements, much of this research has been conducted in low-income countries where mothers are more likely to have nutritional deficiencies than Europe or the United States.
Other investigations into the effectiveness of maternal vitamin and mineral tablets have been observational studies, which are subject to bias and cannot demonstrate cause, only associations.
The current report set out to assess how beneficial maternal supplements are and whether research backs up the sale of these vitamins and minerals. In particular, they concentrated on vitamins A, C, D, and E, iron, and folic acid.
The results of the literature review found that the benefits of folic acid supplementation had the strongest evidence.
A number of studies have shown that folate significantly reduces the chances of neural tube defects, including anencephaly (the baby is born with parts of the brain and skull missing) and spina bifida (the spine is incompletely formed).
The United Kingdom and U.S. guidelines suggest a woman takes 400 micrograms of folic acid from before pregnancy until the 12-week mark. For women at risk of having a child with neural defects, the recommended dose is 5 milligrams.
Vitamin D is produced in the skin when it comes in contact with ultraviolet (UV) light. It plays an essential role in the maintenance of bones by promoting calcium absorption from the gut. Becoming deficient in vitamin D can cause skeletal problems, such as rickets.
The case for vitamin D supplementation was less clear-cut than that for folate; there was little evidence that the vitamin reduced complications associated with pregnancy or birth. A daily dose of 10 micrograms is still recommended during pregnancy and while breastfeeding.
For women who live in colder, cloudier locations (where less UV light is encountered), women with darker skin, or those who are nutrient deficient for other reasons, vitamin D is likely to be more useful.
Most vitamins are ‘an unnecessary expense’
As for the other supplements – A, C, E, and iron – the evidence of health benefits for well-nourished mothers and children was not forthcoming. In fact, excess vitamin A is known to harm the developing baby.