Ultrasound screening showed a sensitivity of 34.9% (33.2-36.6) for LGA and 35.6% (33.5-37.9) for macrosomia, with specificity of 97.4% (97.2-97.6) and 95.6% (95.3-95.9), respectively. Screen-positive pregnancies were significantly less likely to attempt labor (aRR 0.87, 95% CI 0.84-0.90; p<0.001) and more likely to undergo intrapartum cesarean delivery (aRR 1.47, 95% CI 1.30-1.67; p<0.001), with higher risks of composite adverse maternal (aRR 1.43, 95% CI 1.32-1.55; p<0.001) and neonatal (aRR 2.37, 95% CI 1.85-3.05; p<0.001) outcomes. Compared to true-positive cases, false-negative cases were associated with significantly lower rates of induction of labor (aRR 0.74, 95% CI 0.68-0.81; p<0.001), intrapartum cesarean delivery (aRR 0.70, 95% CI 0.59 - 0.83; p<0.001) and composite adverse maternal outcomes (aRR 0.87, 95% CI 0.77-0.98; p<0.032), with no increased risk of adverse neonatal outcomes (aRR 0.77, 95% CI 0.56-1.06; p=0.12). Compared to true-negative cases, false-positive cases experienced higher rates of operative vaginal delivery (aRR 1.29, 95% CI 1.07-1.57; p<0.001), intrapartum cesarean delivery (aRR 1.25, 95% CI 1.0-1.55; p=0.045) and composite adverse maternal outcomes (aRR 1.28, 95% CI 1.11-1.48; p<0.001) with no difference in the risk of adverse neonatal outcomes (aRR 1.35, 95% CI 0.72 - 2.53 p=0.347) CONCLUSION: Routine third-trimester ultrasound screening for suspected LGA and macrosomia demonstrates limited diagnostic performance and appears to generate a labelling effect; whereby obstetric intervention and some adverse outcomes may be influenced more by suspected LGA status than by fetal size itself. These findings raise questions about the benefit of universal LGA screening at term and support consideration of more individualized, risk-based approaches to late-pregnancy assessment.
Lopian et al. (Wed,) studied this question.