title: The association between season of pregnancy and birth-sex among Chinese.
abstract: OBJECTIVE
  although numerous studies have reported the association between birth season and sex ratio, few studies have been conducted in subtropical regions in a non-Western setting. The present study assessed the effects of pregnancy season on birth sex ratio in China.
  
  
  METHODS
  We conducted a national population-based retrospective study from 2006-2008 with 3175 children-parents pairs enrolled in the Northeast regions of China. Demographics and data relating to pregnancy and birth were collected and analyzed. A multiple logistical regression model was fitted to estimate the regression coefficient and 95% confidence interval (CI) of refractive error for mother pregnancy season, adjusting for potential confounders.
  
  
  RESULTS
  After adjusting for parental age (cut-off point was 30 years), region, nationality, mother education level, and mother miscarriage history, there is a significant statistical different mother pregnancy season on birth-sex. Compared with mothers who were pregnant in spring, those pregnant in summer or winter had a high probability of delivering girls (p < 0.05). The birth-sex ratio varied with months.
  
  
  CONCLUSIONS
  Our results suggested that mothers pregnant in summer and winter were more likely to deliver girls, compared with those pregnant in spring. Pregnancy season may play an important role in the birth-sex.
authors.affiliation: Department of Epidemiology, School of Public Health, Medical College of Soochow University, Suzhou, Jiangsu 215123, China. txu6@tulane.edu.
authors.forename: Tan
authors.initials: T
authors.lastname: Xu
authors.affiliation: School of Science and Engineering, Tulane University, New Orleans, LA 70112, USA. dlin5@tulane.edu.
authors.forename: Dongdong
authors.initials: D
authors.lastname: Lin
authors.affiliation: Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, Zhejiang 310051, China. hliang@cdc.zj.
authors.forename: Hui
authors.initials: H
authors.lastname: Liang
authors.affiliation: Longquanyi District First Hospital, Chengdu, Sichuan 610100, China. drizzle-chen@163.com.
authors.forename: Mei
authors.initials: M
authors.lastname: Chen
authors.affiliation: Department of Epidemiology, School of Public Health, Medical College of Soochow University, Suzhou, Jiangsu 215123, China. tongweijun.suda@live.com.
authors.forename: Weijun
authors.initials: W
authors.lastname: Tong
authors.affiliation: The Affiliated People's Hospital of Inner Mongolia Medical University, Hohhot 010110, China. ypmu040@sina.com.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Mu
authors.affiliation: School of Public Health, University of Saskatchewan, Saskatoon SK S7N 5E5, Canada. cindy.feng@usask.ca.
authors.forename: Cindy Xin
authors.initials: CX
authors.lastname: Feng
authors.affiliation: School of Food Science, Guangdong Pharmaceutical University, Zhongshan 528458, China. yongqingg@163.com.
authors.forename: Yongqing
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Center for Science Communication and Health Education Management, National Research Institute for Family Planning, Beijing 100081, China. maria_mei@126.com.
authors.forename: Yumei
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: School of Food Science, Guangdong Pharmaceutical University, Zhongshan 528458, China. wsun3@tulane.edu.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Sun
mesh_terms: D002681:China; D005260:Female; D006801:Humans; D007223:Infant; D016015:Logistic Models; D008297:Male; D036801:Parturition; D011247:Pregnancy; D012044:Regression Analysis; D012189:Retrospective Studies; D012621:Seasons; D012744:Sex Ratio