title: Cross sectional study in China: fetal gender has adverse perinatal outcomes in mainland China.
abstract: BACKGROUND
  The association between fetal gender and pregnancy outcomes has been thoroughly demonstrated in western populations. However, this association has not been thoroughly documented in China. The primary objective of the present study is to determine whether the association of adverse pregnancy and labour outcomes with male fetuses applies to the Chinese population.
  
  
  METHODS
  This cross-sectional hospital-based retrospective survey collected data from thirty-nine hospitals in 2011 in mainland China. A total of 109,722 women with singleton pregnancy who delivered after 28 weeks of gestation were included.
  
  
  RESULTS
  Of these pregnancies, the male-to-female sex ratio was 1.2. The rates of preterm birth (7.3% for males, 6.5% for females) and fetal macrosomia (8.3% for males, 5.1% for females) were higher for male newborns, whereas fetal growth restriction (8.0% for females, 5.4% for males) and malpresentation (4.3% for females, 3.6% for males) were more frequent among female-bearing mothers. A male fetus was associated with an increased incidence of operative vaginal delivery (1.3% for males, 1.1% for females), caesarean delivery (55.0% for males, 52.9% for females), and cephalopelvic disproportion/failure to progress (10.0% for males, 9.2% for female). Male gender was also significantly associated with lower Apgar scores (<7 at 5 min, adjusted odds ratio 1.3, 95% CI 1.0-1.6), as well as a neonatal intensive care unit admission and neonatal death, even after adjustments for confounders (adjusted odds ratio 1.3, 95% CI 1.1-1.5, adjusted odds ratio 1.4, 95% CI 1.1-1.8).
  
  
  CONCLUSIONS
  We confirm the existence of obvious neonatal gender bias and adverse outcomes for male fetuses during pregnancy and labour in our population. Further research is required to understand the mechanisms and clinical implications of this phenomenon.
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. houlei2005@hotmail.com.
authors.forename: Lei
authors.initials: L
authors.lastname: Hou
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. wx1501@aliyun.com.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. liguanghui2007@163.com.
authors.forename: Guanghui
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. lindazou@163.com.
authors.forename: Liying
authors.initials: L
authors.lastname: Zou
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. bjfcyycy@sina.com.
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Department of Obstetrics, Beijing Obstetrics and Gynecology Hospital, Capital Medical University, Beijing, 100026, China. zhangwy9921@hotmail.com.
authors.forename: Weiyuan
authors.initials: W
authors.lastname: Zhang
mesh_terms: D000328:Adult; D001034:Apgar Score; D052178:Cephalopelvic Disproportion / Q000453:epidemiology; D002585:Cesarean Section / Q000706:statistics & numerical data; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D005113:Extraction, Obstetrical / Q000706:statistics & numerical data; D005260:Female; D005317:Fetal Growth Retardation / Q000453:epidemiology; D005320:Fetal Macrosomia / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D007363:Intensive Care Units, Neonatal; D007746:Labor Presentation; D008297:Male; D010343:Patient Admission / Q000706:statistics & numerical data; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D011256:Pregnancy Outcome / Q000453:epidemiology*; D047928:Premature Birth / Q000453:epidemiology; D012189:Retrospective Studies; D012737:Sex Factors; D014593:Uterine Inertia / Q000453:epidemiology; D055815:Young Adult