Background: Folate depletion may result in anaemia during pregnancy.
Objectives: The objective of this review was to assess the effects of folate supplementation in pregnancy on haematological and biochemical parameters and measures of pregnancy outcome. This review did not address the role of periconceptual folate supplementation to diminish the risk of fetal malformation.
Search strategy: A comprehensive electronic search included that of the Cochrane Pregnancy and Childbirth Group trials register.
Selection criteria: Acceptably controlled trials of folate supplementation compared with placebo or no treatment to pregnant women with normal haemoglobin levels.
Data collection and analysis: Trial quality was assessed. Study authors were contacted for additional information when necessary.
Main results: Twenty-one studies were included. The trials varied in quality. Compared to placebo or no supplementation, folate supplementation was associated with increased or maintained serum folate levels (odds ratio 0.18, 95% confidence interval 0.13 to 0.24) and red cell folate levels (odds ratio 0.18, 95% confidence interval 0.09 to 0.38). Folate supplementation was associated with a reduction in the proportion of women with low haemoglobin level in late pregnancy (odds ratio 0.61, 95% confidence interval 0.52 to 0.71) and megaloblastic erythropoiesis (odds ratio 0.65, 95% confidence interval 0.45 to 0.95). Apart from a possible reduction in the incidence of low birthweight, folate supplementation appears to have no measurable effect on any other substantive measures of pregnancy outcome.
Reviewer's conclusions: Folate supplementation during pregnancy appears to improve haemoglobin levels and folate status. There is not enough evidence to evaluate whether folate supplementation has any effect, beneficial or harmful, on clinical outcomes for mother and baby.