Labor induction vs expectant management at 40 weeks: association with Cesarean delivery and intrapartum fetal compromise and role of maternal age and cerebroplacental ratio

OBJECTIVES: To evaluate the clinical course of pregnancies reaching the estimated due date and to determine the relative contribution of maternal and fetal factors, particularly labor induction, fetal Doppler status and maternal age, to the risk of adverse outcome and Cesarean delivery (CD). METHODS: This was a retrospective observational study of singleton pregnancies that reached 40 + 0 weeks' gestation at a single center between December 2020 and December 2025. Maternal characteristics, fetal ultrasound and Doppler indices and delivery outcomes were collected. Variables were compared between pregnancies managed with induction of labor and those managed expectantly at 40 + 0 to 40 + 6 weeks, and between pregnancies undergoing induction of labor and those with spontaneous onset of labor at any gestational age ≥ 40 + 0 weeks. Multivariable logistic regression was used to assess the associations of study variables with intrapartum fetal compromise (IFC), CD for abnormal cardiotocography (CD-CTG) and CD for failure to progress (CD-FP). Effect sizes were expressed as adjusted odds ratios (aORs) with 95% CI. RESULTS: Among 739 pregnancies reaching 40 weeks' gestation, 102 (13.8%) underwent induction of labor at 40 + 0 to 40 + 6 weeks, while 637 (86.2%) were initially managed expectantly. Overall, 393 (53.2%) cases had spontaneous onset of labor and 346 (46.8%) were induced at ≥ 40 + 0 weeks. The rate of CD was significantly higher among pregnancies undergoing induction compared with those managed expectantly at 40 + 0 to 40 + 6 weeks (P < 0.0001) and with those who progressed to spontaneous onset of labor at any gestational age ≥ 40 + 0 weeks (P < 0.0001). On multivariable analysis, induction of labor and cerebroplacental ratio (CPR) multiples of the median (MoM) were independently associated with both IFC (aOR, 2.30 (95% CI, 1.20-4.39); P = 0.0116 and 0.07 (95% CI, 0.02-0.24); P < 0.0001, respectively) and CD-CTG (aOR, 3.10 (95% CI, 1.46-6.56); P = 0.0032 and 0.05 (95% CI, 0.01-0.20); P < 0.0001, respectively). Parity (aOR, 0.48 (95% CI, 0.32-0.72); P = 0.0004), estimated fetal weight centile (aOR, 1.01 (95% CI, 1.00-1.02); P = 0.0018) and induction of labor (aOR, 2.39 (95% CI, 1.54-3.73); P = 0.0001) were associated independently with CD-FP. Maternal age was not associated independently with CD-FP, and its borderline associations with IFC and CD-CTG were no longer significant after adjustment for CPR MoM. CONCLUSIONS: Induction of labor was associated with higher rates of CD at ≥ 40 + 0 weeks, whereas maternal age was not associated independently with adverse intrapartum outcome after adjustment for CPR MoM. Lower CPR MoM was associated independently with IFC and CD-CTG. These findings support further evaluation of individualized management strategies incorporating fetal Doppler assessment in these pregnancies. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.