Objective To externally validate a risk stratified delivery timing model for nulliparous, term, singleton, vertex (NTSV) cesarean reduction using national data.

Design Population based cohort study of NTSV births in US National Vital Statistics System (NVSS) natality files, 2020–2024, using logistic regression for cesarean predictors and risk stratified Monte Carlo simulation (10,000 iterations per strategy and risk group) to evaluate delivery timing policies.

Setting All live births in the US recorded in the NVSS natality files.

Participants NTSV patients with term (37+ weeks) pregnancies and complete gestational age and delivery mode data (N=5 776 412). A sensitivity cohort excluded pre 39 week deliveries and pregnancies with preexisting diabetes or hypertension.

Exposures Delivery timing strategies defined by gestational age and labor onset (elective induction at 39, 40, or 41 weeks, or expectant management to 42 weeks), evaluated within maternal age and body mass index (BMI) risk strata (low: age <35 and BMI <30; moderate: age ≥35 or BMI ≥30; high: age ≥35 and BMI ≥35).

Main Outcomes and Measures Primary outcome was cesarean delivery, measured as the proportion of deliveries completed by cesarean across gestational ages, labor onset types, and age BMI strata. Secondary outcomes included gestational age specific cesarean rates, area under the receiver operating characteristic curve (AUC) for cesarean prediction, and simulated mean cesarean rates with 95% simulation intervals under four delivery timing strategies within each risk group.

Results The overall NTSV cesarean rate was 26.4%. Cesarean Rates were U-shaped across gestational ages, with the lowest rate at 38 weeks (24.9%) and higher rates at 37 weeks (29.8%) and 41–42 weeks (28.1–28.5%). Risk group distribution was 64.9% low, 33.7% moderate, and 1.4% high. Model AUC was 0.65. Induction had higher cesarean rates than spontaneous labor (29.3% vs 24.2%; odds ratio 1.30, 95% confidence interval 1.29-1.30). Monte Carlo simulation favored induction at 39 weeks for high-risk patients (59.3%) and expectant management to 41–42 weeks for low-risk patients (19.1%).

Conclusions and Relevance A risk stratified NTSV labor management model showed external validity in 5.8 million US births and consistently identified risk-specific timing strategies that lowered cesarean rates, supporting individualized delivery timing policies.

Question Among nulliparous, term, singleton, vertex (NTSV) pregnancies, can a previously developed risk stratified delivery timing model identify gestational age and induction strategies that reduce cesarean delivery when applied to US national data?

Findings In this population based retrospective cohort study of 5.8 million NTSV births, external validation showed a U-shaped pattern in cesarean rates across gestational age and indicated that 39 weeks induction minimized cesarean risk for high-risk patients, whereas expectant management to 41–42 weeks minimized risk for low-risk patients.

Meaning This risk stratified delivery timing model reliably identified strategies with lower cesarean delivery rates, supporting its use as a practical framework for counseling and institutional policy.

The authors have declared no competing interest.

This study did not receive any funding

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study used de identified published CDC natality data only.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors