THE ASSOCIATION OF FETAL SEX WITH THE RATE OF CESAREAN-SECTION

OBJECTIVE: Our purpose was to evaluate the rate of cesarean deliveries according to fetal sex. STUDY DESIGN: We evaluated method of delivery , indication for cesarean section, and infant outcome according to fet al 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 c esarean section rate was 13.2% among 1246 women carrying male fetuses compared with 9.6% among 1193 women carrying female fetuses (odds rati o 1.4, 95% confidence interval 1.1 to 1.8). There was a 30% increase i n cesarean sections for failure to progress (odds ratio 1.3, 95% confi dence interval 1.0 to 1.8) and a 70% increase in those for fetal distr ess (odds ratio 1.7, 95% confidence interval 1.0 to 3.0). When adjuste d for gestational age and fetal size, male fetal sex no longer predict ed the risk of cesarean delivery for failure to progress (adjusted odd s ratio 1.04, 95% confidence interval 0.8 to 1.4) but continued to pre dict the risk of cesarean section for fetal distress (adjusted odds ra tio 2.2, 95% confidence interval 1.3 to 4.0). Among infants delivered by cesarean section for fetal distress, males were more than three tim es as likely than females to have an Apgar score less than or equal to 7 at both 1 and 5 minutes. CONCLUSION: Increased cesarean deliveries for failure to progress among women with male fetuses is related to th e larger size of males, whereas the increase for fetal distress is not , and may relate to other developmental differences between male and f emale fetuses.