The frequency of twin pregnancies increased in a Chilean hospital associated with periconceptional flour folic acid supplementation

A significant increase in the frequency of twins has been described in the literature as a secondary effect of perinatal supplementation with folic acid. To verify if the frequency of twins increased in a Chilean hospital, after the start of flour folic acid supplementation. The frequency of twins was compared in the University of Chile Clinical Hospital, before and after the start of flour fortification with folic acid. There was a 34% increase in the frequency of twins during the post fortification period (2001-2004) as compared with the previous period (1998-2000). A decrease in the frequency of male twins, when compared with single newborns, was also observed in the post fortification period. There was a higher frequency of stillborns among twins, when compared with single newborns. The frequency of twin pregnancies increased after flour folic acid supplementation in sample of Chilean population.