Periconceptional folic acid/multivitamin supplementation and twin pregnancy

Objective: Results of our previous randomized controlled trial suggested an increase of twin pregnancies that was associated with the use of a multivitamin that contained folic acid during the periconceptional period. These findings were confirmed by US and Swedish studies, but not in the Chinese population. The aim of this analysis is to evaluate this possible association in a population-based data set. Study design: The population-based large control data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (1980-1996) was evaluated. Control pregnant women were differentiated according to pre- and postconceptional supplementation of folic acid (in general 6 mg), multivitamins that contained 0.1 to 1.0 mg folic acid, folic acid plus multivitamin, and the prevalence of twin pregnancies was compared with the prevalence of twin pregnancies in the women who did not received supplements as referent. Results: Of 38,151 women, 395 women gave birth to twins. The prevalence of twin births was 0.78% in the unsupplemented group; the rate of twin pregnancies was 1.52% after the preconceptional supplementation (adjusted odds ratio, 1.80; 95% CI, 1.14-2.85). The proportions of twin pregnancies were 1.14%, 1.45%, and 2.00% after the postconceptional folic acid, multivitamin, and folic acid plus multivitamin supplementation, respectively. Conclusion: Our findings suggest that both pre- and postconceptional supplementation of a high dose of folic acid and multivitamins are associated with a slight increase of the incidence of twin pregnancies. (C) 2004 Elsevier Inc. All rights reserved.