title: Periconceptional Multivitamin Supplementation Containing Folic Acid and Sex Ratio at Birth in a Chinese Population: a Prospective Cohort Study.
abstract: BACKGROUND
  To determine whether periconceptional use of multivitamin supplements containing folic acid increases the occurrence of male births in a Chinese population.
  
  
  METHODS
  A prospective cohort study was carried out in 18 counties in four provinces of China. Participants were naturally and voluntarily divided into an intervention group (who took a multivitamin pill containing folic acid, n = 25,418) and a control group (who did not take any multivitamin, n = 26,580). Multivitamin supplements containing folic acid was ascertained before pregnancy. Pregnant women were followed through the first trimester of pregnancy and the outcome of pregnancy (i.e. livebirth, stillbirth, or fetal death; sex at birth) was recorded.
  
  
  RESULTS
  A total of 52,043 pregnancies and 51,998 births were recorded between September 2000 and August 2002. The proportion of males born to women who did and did not take the multivitamin were 54.8% (n = 13,935) and 54.0% (n = 11,483), respectively. The male to female sex ratios at birth among women who did and did not take the multivitamin were 117:100 and 121:100, respectively. The risk ratio was 1.03 [95% confidence interval 0.99, 1.06] after adjusting for confounding factors.
  
  
  CONCLUSIONS
  These findings suggest that periconceptional multivitamin supplementation containing folic acid is not associated with an increased likelihood of male births in a Chinese population. However, these results may have been affected by induced abortion or selective termination of pregnancy, and the findings must therefore be cautiously interpreted.
authors.affiliation: Institute of Population Research, Peking University, Beijing, China.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Institute of Population Research, Peking University, Beijing, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Pei
authors.affiliation: Institute of Population Research, Peking University, Beijing, China.
authors.forename: Gong
authors.initials: G
authors.lastname: Chen
authors.affiliation: Institute of Population Research, Peking University, Beijing, China.
authors.forename: Xinming
authors.initials: X
authors.lastname: Song
authors.affiliation: Institute of Population Research, Peking University, Beijing, China.
authors.forename: Jilei
authors.initials: J
authors.lastname: Wu
authors.affiliation: School of Public Health, Peking University, Beijing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Ji
mesh_terms: D000028:Abortion, Induced / Q000706:statistics & numerical data*; D000328:Adult; D002681:China / Q000453:epidemiology; D019587:Dietary Supplements; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011159:Population Surveillance; D016742:Preconception Care / Q000379:methods* / Q000706:statistics & numerical data; D011247:Pregnancy; D015995:Prevalence; D011446:Prospective Studies; D012744:Sex Ratio; D016896:Treatment Outcome; D014815:Vitamins / Q000008:administration & dosage*
chemical_list: D014815:Vitamins; D005492:Folic Acid
keywords: Chinese population; multivitamin supplements containing folic acid; prospective cohort study; sex ratio at birth