The effect of periconceptional multivitamin/trace element supplementation on pregnancy outcomes was evaluated in a randomised controlled trial. The final data-base included 5,502 females with confirmed pregnancy. A multivitamin including 0.8 mg folic acid or a trace element were supplemented for at least 28 days before conception and continuing for at least until the second missed menstrual period. Number of pregnancies, terminations of pregnancies, four types of fetal deaths, livebirths including low birth weight, preterm birth and sex ratio were analysed. Periconceptional multivitamin supplementation increased fertility (higher rates of cumulative conceptions and multiple births), had no significant effect on the rate of different groups of fetal deaths, low birth weight and preterm birth in singletons. This primary preventive method can reduce the occurrence and recurrence of neural-tube defects and had no other significant effect on pregnancy outcomes except multiple births.