Objective: To determine whether a supplement of folic acid given preconceptionally or early in pregnancy had any influence on, birth weight, incidence of preterm labour, low birth weight and small for gestational age. Furthermore, the aim was to elucidate, whether the outcome differed following the administration of two different dosages of folic acid, namely 2.5 and 1.0 mg.
Material: All women in the childbearing age living on the island of Funen, Denmark (population 500,000) were offered a supplement of folic acid over a period of 3 years and 3 months. 14,021 women, who gave birth to 13,860 single-born and 325 multiborn children, were registered. A total of 8184 women took part in the double-blind randomized trial: 2310 had a supplement of folic acid without being randomized and 2721 women received no folic acid supplement. No information regarding the use of folic acid was available in 806 pregnancies. Abortions (512) were excluded.
Results and conclusions: A supplement 1.0 mg folic acid had the same effect as 2.5 mg. The effects of supplementing the diet with folic acid given preconceptionally or in the first half of pregnancy in an affluent Northern country were a slight increase of birth weight and a decrease in the incidence of preterm labour, infants with low birth weight and small for gestational age. The greatest effect was seen in the groups receiving folic acid preconceptionally.