Mothers-to-be have long been advised to take the supplement – a form of Vitamin B – in order to protect their unborn children from developing conditions such as spina bifida as well as from being born early.

A major study published three years ago suggested that women could reduce their risk of having premature babies by more than half if they started taking folic acid a year before conceiving, preventing thousands of deaths a year.

But a new analysis of the dietary records of pregnant Norwegian women has found that taking folic acid or eating foods rich in folate, such as broccoli, chickpeas and Brussels sprouts, did not protect them against giving birth prematurely.

The study of 955 premature babies – born between 22 and 36 weeks - and 18,075 controls among the Norwegian Mother and Child Cohort Study found “no significant association between folate supplementation and spontaneous preterm delivery”.

Verena Senpiel, who presented the study at the Society for Maternal-Fetal Medicine’s annual meeting in San Fransisco, said: “Sufficient folate intake has been studied as a possible protecting factor against spontaneous preterm delivery with conflicting results.

“Preterm delivery is the major cause of perinatal mortality and morbidity worldwide and still difficult to predict and prevent. So when a recent American study found that preconceptional folate supplementation could reduce the risk for early spontaneous preterm delivery 50-70 per cent we hoped to confirm these findings in another big cohort study.”

A spokesman for the Royal College of Obstetricians and Gynaecologists said the study should not deter pregnant women from taking folic acid.

“We would strongly recommend folic acid for the first trimester, for the prevention of birth defects.”

Andy Cole, Chief Executive of Bliss, added: “While this is interesting research, there is very good evidence that folate aids foetal development and has health benefits to the mother.

“Further research is needed before a conclusion can be made as to whether folate impacts on preterm birth and we would not recommend that women stop taking these supplements.”

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By Martin Beckford,
Health Correspondent