Multivitamins for healthy pregnant women are a waste of time. Doctors should say so

In my daily practice, I get frequent questions from pregnant women regarding what constitutes optimal nutrition, as rare is the lady who doesn’t want to give her baby the best possible start.

Generally speaking, of course, women do need to eat as healthy a diet as possible, balanced in macro and micronutrients, in order to ensure that the necessary chemical building blocks are available for the baby.

Manufacturers of multivitamins, particularly those ‘designed for the pregnant woman’, often make subtle claims that suggest better health outcomes with their use. The argument is often made that many patients do not eat a balanced diet and hence supplementation ensures that deficiency does not occur.

At first glance it would appear they are on to something. We are, however, living in an era of evidence-based medicine, and unless there is evidence to recommend a particular supplement there is no need to prescribe it. Pregnancy is a physiological state, and problems arise once it is medicalised unnecessarily. A recent paper has reviewed the literature on the subject and, despite the explosion that has occurred in the last few years in terms of published research on all facets of pregnancy, its conclusions have merely confirmed what is already recommended.

Common pregnant multivitamins contain a range of substances, among them minerals and vitamins such as iron, folic acid, vitamin D, calcium, vitamin C, vitamin E, in varying amounts, all of which have been touted as essential to a healthy pregnancy.

In certain clinical situations, supplementation in pregnancy is essential. Folic acid supplementation in all women has been shown to decrease the risk of neural tube defects, eg spina bifida, by up to 70 per cent. In women with epilepsy, on anti-seizure medication and others, a higher dose of folic acid is required in order for the preventative effect to be realised.

Iron supplementation is required for women with pre-existing anaemia or women on the verge of anaemia as anaemia is associated with adverse pregnancy outcomes, including low birth weight and stillbirth.

In women with calcium-wasting diseases including kidney disease, calcium supplementation is essential. Indeed in women who have previously developed preeclampsia, calcium supplements in the presence of deficiency have been shown to effectively decrease the risk of a recurrence significantly.

The role of vitamin D supplementation is more nuanced; knowledge is accumulating all the time and there does seem to be a relationship between better vitamin D stores in the mother and a lower incidence of rickets in children, hence justifying its use.

What of healthy women though? The recently re-reviewed evidence suggests no benefit from the routine supplementation of any of the aforementioned apart from folic acid and vitamin D.

This new evidence is in line with existing recommendations by NICE and the Royal College of Obstetricians and Gynaecologists, to supplement only with folic acid and vitamin D.

There is no scientific basis for the concept of ‘dietary gaps’ to justify multivitamin consumption in healthy pregnant women. Either you consume adequate amounts of an essential nutrient, or you have a deficiency, something difficult to achieve unless diet is suboptimal or there is a health issue.

Some myopic individuals won’t accept this. I find it astounding how some people reject as ‘absolute nonsense’ the idea that pregnant women should only taken supplements with proven clinical effects.

Some will argue that there is no harm in prescribing multivitamins to all pregnant women, especially given that many patients derive comfort from knowing that they are doing ‘all they can’ to ensure a healthy pregnancy.

I would argue that in the era of evidence-based medicine, non-paternalism and patient empowerment by knowledge, it is not my job to service the profits of supplement companies or to encourage patients to produce very expensive, nutritionally dense urine.

It is better, I think, to educate patients on what constitutes a healthy diet. ‘Let food be thy medicine’ — a useful saying on the subject of multivitamins.