(666) Diagnostic Performance of Three Methods of Fetal Growth Restriction Diagnosis

Recent guidelines changed the diagnostic criteria for fetal growth restriction (FGR) from estimated fetal weight (EFW) < 10%ile alone to EFW and/or abdominal circumference (AC) < 10%ile. Prior studies suggested this change would not substantially affect the number of pregnancies diagnosed with FGR. This study compares 3 methods of FGR diagnosis.

Study Design:

This retrospective cohort study classified three groups of women delivering at our institution based on timing of how we diagnosed FGR: Group 1 (7/1/17-6/30/18; EFW < 10%ile), Group 2 (4/1/20-3/31/21; EFW < 10%ile or EFW 10-19%ile and AC < 5%ile), and Group 3 (8/1/21-7/31/22; EFW and/or AC < 10%ile). Multifetal gestations and fetuses with major anomalies were excluded. Cases of neonatal small for gestational age (SGA) were also identified in each time period. The primary outcome was prevalence of FGR among all deliveries in each time period. Test performance characteristics of the three methods of FGR diagnosis for predicting SGA were evaluated.

Results:

320 pregnancies with FGR were identified (n=44 Group 1, n=96 Group 2, n=180 Group 3). Maternal characteristics were similar between groups (Table 1). For groups 1, 2 and 3 respectively, the prevalence of FGR was 1.16%, 2.74% and 4.82% (p< 0.0001), and the prevalence of SGA was 3.39%, 4.44% and 4.53% (p=0.02). Test performance characteristics of each approach are shown in Table 2.

Conclusion:

Application of the newest diagnostic criteria for FGR resulted in a quadrupling of the rate of FGR diagnosis. Though the prevalence of FGR diagnosis with the newest criteria was similar to the prevalence of SGA, this approach identified less than half of neonates with SGA. Given this substantial increase in diagnoses, most of which are false positives, further investigation regarding resource utilization and neonatal outcomes is warranted.