Maternal folic acid supplementation and more prominent birth weight gain in twin birth compared with singleton birth: a cross-sectional study in northwest China

Objective: To investigate the association of folic acid (FA) supplementation with birth weight, the risk of small for gestational age (SGA) and low birth weight (LBW) in singleton and twin pregnancy. Design: A population-based cross-sectional survey. Setting: Twenty counties and ten districts in Shaanxi Province of northwestern China, 2013. Participants: 28 174 pregnant women with their infants, covering 27 818 single live births and 356 twin live births. Results: The prevalence of FA supplementation in singletons and twins was 63 center dot 9 and 66 center dot 3 %. The mean birth weight was 3267 (sd459 center dot 1) g, 2525 (sd534 center dot 0) g and 2494 (sd539 center dot 5) g; the prevalence of SGA was 14 center dot 3, 51 center dot 4 and 53 center dot 4 %; the prevalence of LBW was 3 center dot 4, 42 center dot 4 and 46 center dot 6 % among singleton, twin A and twin B, respectively. Compared with non-users, women with FA supplementation were (beta 17 center dot 3, 95 % CI 6 center dot 1, 28 center dot 4;beta 166 center dot 3, 95 % CI 69 center dot 1, 263 center dot 5) associated with increased birth weight, lower risk of SGA (OR 0 center dot 85, 95 % CI 0 center dot 80, 0 center dot 92; OR 0 center dot 45, 95 % CI 0 center dot 30, 0 center dot 68) and LBW (OR 0 center dot 82, 95 % CI 0 center dot 71, 0 center dot 95; OR 0 center dot 50, 95 % CI 0 center dot 33, 0 center dot 75) in singletons and twins, and more prominent effects in twins. Moreover, there were significant interactions between FA supplementation and plurality on birth weight, SGA and LBW. Conclusions: The present study suggests the association of periconceptional 0 center dot 4 mg/d FA supplementation with increased birth weight and reduced risk of SGA and LBW in both singletons and twins, and this association may be more prominent in twins.