Folate unlikely to increase chance of twins, says study

Increased risk of having twins has previously been an argument against the introduction of fortification of flour with folic acid.

Recent reports suggest that advice to women to take folic acid supplements in order to prevent their babies from developing spina bifida has not been effective. In contrast, fortification of flour with the B vitamin in countries like the US and Canada has had significant results. Yet many governments are wary of potential side effects of such a policy on different population groups.

The new Norwegian research suggests that folic acid supplements is unlikely to increase chances of having twins, one of the previously cited potential side effects.

The team from the University of Bergen studied data on use of folate supplements and multivitamins from more than 176,000 Norwegian women who gave birth between 1998 and 2001.

After exclusion of known IVF pregnancies, and accounting for underreporting of both IVF pregnancies and folate use, there was no evidence of higher chances of twins, said the researchers in this month's issue of Epidemiology​ (vol 16, issue 2, pp201-5).

The researchers initially found that overall, women who took folic acid before pregnancy were 59 per cent more likely to have twins than women who did not take the supplements.

However, when they excluded those who had not conceived naturally, there was only a very weak link between vitamin use and chances of twins.

Women who undergo IVF treatment are much more likely to have multiple births. The study also found them much more likely to take folic acid before getting pregnant.

This increased use of folic acid by women on IVF could explain the link between folate and twin pregnancies found in earlier studies.

A Swedish study previously concluded that folic acid was associated with a 45 per cent greater chance of having twins.