Increased rate of cesarean section in primiparous women aged 40 years or more: a single-center study in Japan

To investigate perinatal outcomes in late primiparous women aged 35-39 and >= 40 years. Our main research question: "Was the rate of cesarean section similar between these 2 groups of advanced maternal age?" Primiparous women aged >= 35 years, who delivered in our center between April 2004 and March 2007, were enrolled in this study. They were divided into two groups: women aged 35-39 years and those aged >= 40 years. Antenatal complications, deliveries, and neonatal outcomes were analyzed. Fetal abnormalities, abortions, and multiple gestations were excluded. We assessed 752 cases (35-39 years, 610 cases; >= 40 years, 142 cases). Incidence of cesarean section (CS) was significantly higher in pregnant women aged >= 40 years (P < 0.01). The CS rate amounted to 50.0% of all deliveries in this age group. Among patients with labor deliveries, the CS rate was also significantly higher in the older age group (P < 0.05). With regard to indication for CS with labor deliveries, the rate of non-progressive labor/dystocia was 19.4% in primiparous women aged >= 40 years and 11.0% in those aged 35-39 years, respectively (P < 0.05). In contrast, the rates of antenatal complications were not different between the two groups, except for gestational diabetes or leiomyoma. No significant differences between the two groups could be found for neonatal outcomes such as birth weight, Apgar score, and admission to neonatal intensive care unit. CS rate was 50.0% in primiparous women aged >= 40 years. In addition, CS caused by dystocia was almost twice as frequent in primiparous women aged >= 40 years as in women aged 35-39 years. Among late pregnancies, primiparous women aged 40 years and older had higher risk of CS.