Routine 36-week scan: prediction of small-for-gestational-age neonate.

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Diagnostic Ultrasound

Background:

• Accurate prediction of small-for-gestational-age (SGA) neonates is crucial for optimizing perinatal outcomes.
• Routine third-trimester ultrasonographic estimated fetal weight (EFW) is used to assess fetal growth.
• The optimal timing and methodology for EFW screening for SGA detection require further investigation.

Purpose of the Study:

• To compare the predictive performance of EFW at different gestational age windows (31–33 vs. 35–36 weeks) for SGA delivery.
• To evaluate EFW's predictive accuracy for SGA versus fetal growth restriction (FGR) at birth.
• To assess the benefit of combining EFW with maternal risk factors versus EFW alone for SGA prediction.

Main Methods:

• Retrospective analysis of prospectively collected data from 21,676 women (31–33 weeks) and 107,875 women (35–36 weeks).
• EFW calculated using Hadlock formula; SGA defined as birth weight <10th or <3rd percentile.
• FGR defined as birth weight <10th percentile with Doppler anomalies; AUC compared for different screening strategies.

Main Results:

• Screening at 35–36 weeks gestation demonstrated higher predictive performance for SGA than at 31–33 weeks.
• Predicting FGR or using birth weight <3rd percentile improved detection rates compared to SGA (<10th percentile).
• A combined model of EFW and maternal risk factors significantly outperformed EFW alone for SGA prediction.

Conclusions:

• Routine third-trimester ultrasound screening for SGA is most effective between 35 and 36 weeks gestation.
• Combining EFW with maternal demographic characteristics and medical history enhances patient-specific risk estimation.
• These findings support optimized screening protocols for identifying fetuses at risk of growth abnormalities.