This study evaluates the effects of supplementation with 4 versus 0.4 mg of folic acid per day at preconception and during the first three months of pregnancy on recurrence of cleft lip and palate. Up to 6000 women will be randomly assigned to 4 versus 0.4 mg groups. The primary aim is to compare the recurrence rates in the offspring of trial mothers in the two groups. Secondary aims are to compare the two groups on several outcomes including miscarriage, twinning, pre-eclampsia, serum and red cell folate levels, severity of oral clefts and occurrence of other birth defects in the offspring of trial mothers, and birth weight and gestational age of trial babies, and to compare the recurrence in the two groups to that in historic controls.