title: The association of fetal sex with the rate of cesarean section.
abstract: OBJECTIVE
  Our purpose was to evaluate the rate of cesarean deliveries according to fetal sex.
  
  
  METHODS
  We evaluated method of delivery, indication for cesarean section, and infant outcome according to fetal sex in 2439 low-risk nulliparous women in spontaneous labor. Crude odds ratios and 95% confidence intervals were calculated. Confounding was controlled with use of logistic regression.
  
  
  RESULTS
  The overall cesarean section rate was 13.2% among 1246 women carrying male fetuses compared with 9.6% among 1193 women carrying female fetuses (odds ratio 1.4, 95% confidence interval 1.1 to 1.8). There was a 30% increase in cesarean sections for failure to progress (odds ratio 1.3, 95% confidence interval 1.0 to 1.8) and a 70% increase in those for fetal distress (odds ratio 1.7, 95% confidence interval 1.0 to 3.0). When adjusted for gestational age and fetal size, male fetal sex no longer predicted the risk of cesarean delivery for failure to progress (adjusted odds ratio 1.04, 95% confidence interval 0.8 to 1.4) but continued to predict the risk of cesarean section for fetal distress (adjusted odds ratio 2.2, 95% confidence interval 1.3 to 4.0). Among infants delivered by cesarean section for fetal distress, males were more than three times as likely than females to have an Apgar score < or = 7 at both 1 and 5 minutes.
  
  
  CONCLUSIONS
  Increased cesarean deliveries for failure to progress among women with male fetuses is related to the larger size of males, whereas the increase for fetal distress is not, and may relate to other developmental differences between male and female fetuses.
authors.affiliation: Department of Obstetrics and Gynecology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: E
authors.initials: E
authors.lastname: Lieberman
authors.forename: J M
authors.initials: JM
authors.lastname: Lang
authors.forename: A P
authors.initials: AP
authors.lastname: Cohen
authors.forename: F D
authors.initials: FD
authors.lastname: Frigoletto
authors.forename: D
authors.initials: D
authors.lastname: Acker
authors.forename: R
authors.initials: R
authors.lastname: Rao
mesh_terms: D001724:Birth Weight; D002585:Cesarean Section / Q000706:statistics & numerical data; D005260:Female; D005316:Fetal Distress / Q000601:surgery; D005865:Gestational Age; D006257:Head / Q000033:anatomy & histology; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D008297:Male; D007744:Obstetric Labor Complications / Q000601:surgery; D016017:Odds Ratio; D011247:Pregnancy; D012306:Risk; D012737:Sex Factors