In the study, 35,897 women reported the multi-vitamins they took during the six weeks just before and six weeks after becoming pregnant.
Compared to women who did not take multi-vitamins, women with pre-pregnancy body mass index (BMI) scores no higher than 25 who took multi-vitamins regularly before and after becoming pregnant were 16 percent less likely to have a pre-term birth, and 20 percent less likely to have pre-term labor.
Women of any BMI who took multi-vitamins before and after becoming pregnant were 17 percent less likely to have babies that were small for their gestational age.