Utility of ultrasound surveillance of fetal growth in patients with marginal or velamentous cord insertion

Abstract Introduction Abnormal cord insertion into the placenta (marginal and velamentous) has been associated with fetal growth restriction (FGR), leading some to recommend evaluation of fetal growth in the third trimester. The purpose of this study was to evaluate the timing of ultrasound surveillance in patients with marginal cord insertion (MCI) or velamentous cord insertion (VCI). Methods Retrospective cohort of singleton pregnancies diagnosed with isolated MCI or VCI prior to 24 weeks at a single center from September 2021 to May 2025. Outcomes considered were diagnosis of FGR (estimated fetal weight [EFW] or abdominal circumference [AC] <10 percentile) and oligohydramnios (amniotic fluid index [AFI] ≤ 5 cm). The number of ultrasound scans needed to identify one abnormality (NNS) and 95% confidence interval (CI) were calculated for scans performed at 24+0–31+6 weeks and ≥ 32 weeks. Results Among 248 patients with MCI meeting inclusion criteria, 710 ultrasounds were performed ≥ 24 weeks. A total of eight (3.2%) cases of FGR were diagnosed. Prior to 32 weeks, four cases of FGR were diagnosed (NNS 37.2, 95% CI, 14.9–135.8); however, half of these resolved on follow‐up ultrasound. After 32 weeks, the NNS to identify one case of FGR was 80.5 (95% CI, 31.7–294.6); FGR persisted on subsequent ultrasound(s) for all of these cases. Among 65 patients with VCI meeting inclusion criteria, 151 ultrasounds were performed. Two cases of FGR were diagnosed, both ≤ 32 weeks. The NNS to diagnose one case from 24+0–31+6 weeks was 26.5 (95% CI, 7.7–217.2). There were no cases of oligohydramnios diagnosed in either sample. Conclusion For patients with MCI, half of FGR cases diagnosed ≤32 weeks resolved prior to delivery and were thus likely false‐positives, while all cases of FGR diagnosed ≥32 weeks persisted; thus, a single ultrasound at 32–36 weeks may be considered as a resource‐efficient monitoring approach. Among patients with VCI, both FGR cases ( n = 2) were diagnosed at 30–32 weeks; initiation of growth ultrasounds after 28 weeks is recommended, although recommendations cannot be made regarding frequency based on our study.