Screening increases intervention without neonatal benefit Routine late-pregnancy ultrasound labeling of fetal largeness increased obstetric intervention without clear neonatal benefit.
*Retrospective cohort with diagnostic accuracy analysis; Level 2 (OCEBM).

Citation

Lopian M, Ulusoy CO, Mohamed D, Segal E, Khalil A. Screening for large-for-gestational-age neonates at term. American Journal of Obstetrics & Gynecology. 2026.

Background

Large babies have higher delivery risks, but ultrasound weight estimates near term are imperfect. This study examined whether routine screening helps outcomes or mainly changes clinician behavior.

Patients

21,743 singleton pregnancies with routine ultrasound at 35 to 37 weeks at one London tertiary center. Excluded: major fetal anomalies, genetic abnormalities, or missing outcome data.

Intervention

Screen-positive ultrasound: estimated fetal weight at or above the 90th percentile.

Control

Screen-negative ultrasound; analyses also compared false-positive with true-negative and false-negative with true-positive groups.

Outcome

Detection of large-for-gestational-age or birthweight over 4000 g; delivery mode; maternal and neonatal composite adverse outcomes.

Follow-up Period

From ultrasound to delivery, about 20 to 23 days.

Results

Finding Result
Detection of large-for-gestational-age birth Sensitivity 34.9% (95% CI 33.2 to 36.6); specificity 97.4% (95% CI 97.2 to 97.6)
Attempted labor after positive screen RR 0.87 (95% CI 0.84 to 0.90)
Intrapartum cesarean after positive screen RR 1.47 (95% CI 1.30 to 1.67); approximate NNH 22
Maternal composite adverse outcome after positive screen RR 1.43 (95% CI 1.32 to 1.55); approximate NNH 12
False-positive screen: maternal composite outcome RR 1.28 (95% CI 1.11 to 1.48); no neonatal benefit
RR: relative risk. NNH: number needed to harm, calculated from unadjusted event rates.
Composite maternal outcomes included intrapartum cesarean delivery, which likely contributed substantially to the composite increase. Results were adjusted observational analyses.

Limitations

Retrospective, single-center design limits causal inference. Clinicians knew ultrasound results, which was central to the labeling effect but may confound management. Residual confounding, local protocols, other ultrasound findings, and record misclassification may affect results.

Funding

Funding not reported; authors declared no conflicts.

Clinical Application

Do not use routine term fetal-size screening alone to trigger intervention; counsel patients about limited accuracy and uncertain neonatal benefit.