title: Folic acid supplementation, preconception body mass index, and preterm delivery: findings from the preconception cohort data in a Chinese rural population.
abstract: BACKGROUND
  Folic acid (FA) supplementation before and during the first trimester can reduce the risk of occurrence of preterm delivery (PTD). Preconception body mass index (BMI) is also associated with PTD. This study aimed to investigate the combined effect of FA supplements and preconception BMI on the risk of PTD.
  
  
  METHODS
  The data of a cohort from 2010-2011 that was obtained through a preconception care service in China was used (including 172,206 women). A multivariable regression model was used to investigate the association between maternal preconception conditions and the risk of PTD. The interaction of preconception BMI and FA supplementation was measured by a logistic regression model.
  
  
  RESULTS
  Taking FA supplements in the preconception period or in the first trimester reduced the risk of PTD (odds ratio [OR] = 0.58 and OR = 0.61, respectively). Women with an abnormal BMI had an increased risk of PTD (OR = 1.09, OR = 1.10, and OR = 1.17 for underweight, overweight, and obese, respectively). Preconception BMI showed an interaction with the protective effect of FA supplementation for PTD. With regard to the interaction of FA supplementation, the adjusted odds ratio (aOR) was 0.57 (95% CI: 0.51, 0.64) in underweight women, 0.85 (95% CI: 0.73, 0.98) in overweight women, and 0.77 (95% CI, 0.65, 0.91) in obese women. Preconception BMI also showed an interaction with the time of FA supplementation. Women with a normal BMI who began to take FA supplements in the preconception period had the lowest risk of PTD (aORs: 0.58 vs. 0.65 beginning in the first trimester). The aORs at preconception and the first trimester in the underweight group were 0.56 vs. 0.60. The aORs at preconception and the first trimester were 0.94 vs. 0.65 and 1.15 vs. 0.60 in the overweight and obesity groups, respectively.
  
  
  CONCLUSIONS
  In our study, FA supplements reduced the risk of PTD, while abnormal BMI raised the risk of PTD, although higher BMI categories did not have this higher risk once adjusted analysis was conducted. The protective effect of FA supplementation for PTD was reduced in women with overweight or obesity. To get better protection of FA supplementation, women with normal BMI or underweight should begin to use in preconception, while women with overweight or obesity should begin to use after conception.
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. wyy@e-health.org.cn.|Graduate School of Peking Union Medical College, No. 9, Dongdansantiao, Dongcheng District, Beijing, 100730, China. wyy@e-health.org.cn.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. zongfu_cao@163.com.|Graduate School of Peking Union Medical College, No. 9, Dongdansantiao, Dongcheng District, Beijing, 100730, China. zongfu_cao@163.com.
authors.forename: Zongfu
authors.initials: Z
authors.lastname: Cao
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. pengzuoqi@sohu.com.
authors.forename: Zuoqi
authors.initials: Z
authors.lastname: Peng
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. xinxiaona@e-health.org.cn.|Graduate School of Peking Union Medical College, No. 9, Dongdansantiao, Dongcheng District, Beijing, 100730, China. xinxiaona@e-health.org.cn.
authors.forename: Xiaona
authors.initials: X
authors.lastname: Xin
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. zhangya@e-health.org.cn.
authors.forename: Ya
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. angela-yy65@hotmail.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Yang
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. heyuan8506@126.com.
authors.forename: Yuan
authors.initials: Y
authors.lastname: He
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. gracexjh@163.com.
authors.forename: Jihong
authors.initials: J
authors.lastname: Xu
authors.affiliation: National Research Institute for Family Planning, No. 12, Dahuisi Road, Haidian District, Beijing, 100081, China. genetic88@126.com.|Graduate School of Peking Union Medical College, No. 9, Dongdansantiao, Dongcheng District, Beijing, 100730, China. genetic88@126.com.
authors.forename: Xu
authors.initials: X
authors.lastname: Ma
mesh_terms: D000328:Adult; D044466:Asian People; D015992:Body Mass Index; D002681:China / Q000453:epidemiology; D019587:Dietary Supplements / Q000592:standards*; D005260:Female; D005492:Folic Acid / Q000494:pharmacology*; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D009765:Obesity / Q000453:epidemiology*; D016017:Odds Ratio; D016742:Preconception Care / Q000592:standards; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D018570:Risk Assessment; D012424:Rural Population; D013851:Thinness / Q000453:epidemiology*; D055815:Young Adult
chemical_list: D005492:Folic Acid