(840) Impact of Nonstress Test in Antenatal Surveillance of Fetal Growth Restriction

Antenatal surveillance of fetal growth restriction (FGR) includes a combination of Doppler velocimetry of various fetal vessels and nonstress testing (NST). However, due to time constraints and resource availability, some protocols may opt for an ultrasound-only approach. Our study aimed to determine if the inclusion of NST to antenatal surveillance in FGR decreases the probability of composite neonatal adverse outcomes (CNAO).

Study Design:

We performed a retrospective cohort study of FGR patients from 2022-2024. In 2023, the institutional protocol for FGR changed from as-needed NST to NST required for all patient encounters after 32 weeks. Those managed after the change served as the study group; those prior were controls. Ultrasound surveillance for both groups included q3-4-week growth evaluation and weekly biophysical profile with umbilical artery S/D ratio evaluation. Singleton pregnancies with FGR (EFW or AC < 10% for GA by Hadlock et al curve) who delivered ≥ 24 weeks were included. CNAO was a composite of Apgar score < 7 at 5 min, mechanical ventilation > 24 hours, neonatal seizure, culture-proven neonatal sepsis, intracranial hemorrhage, and stillbirth or neonatal death. To assess the impact of the addition of routine NST, a 3:1 group allotment (study: control) was used. Bayesian analysis was used to calculate the posterior relative risk and the posterior probability of risk reduction.

Results:

There were 903 individuals included for analysis, with 214 in the control and 689 in the study group. Baseline characteristics were similar between groups except for ethnicity, chronic hypertension, and gestational diabetes. CNAO occurred in 4.2% of the control group, and 5.5% in the study group (pRR 1.36, 95% CrI 0.72 – 2.91) with 20% posterior probability of any reduction in CNAO (80% probability of increasing). The number needed to harm in our cohort was 77.

Conclusion:

In our cohort, the addition of NST to antenatal FGR surveillance did not significantly change CNAO. This information may help develop FGR surveillance protocols while balancing the risk of potential iatrogenic harm.