Definitions matter: detection rates and perinatal outcome for infants classified prenatally as having late fetal growth restriction using SMFM biometric vsISUOG/Delphi consensus criteria
Authors: Schreiber V. , Hurst C. , da Silva Costa F. , Stoke R. , Turner J. , Kumar S. 
Published: July 2022

Objectives

Fetal growth restriction (FGR) is often secondary to placental dysfunction and is suspected prenatally based on biometric or circulatory abnormalities detected on ultrasound. The aims of this study were to compare the screening performance of the Society for Maternal–Fetal Medicine (SMFM) biometric criteria (estimated fetal weight (EFW) or abdominal circumference (AC) < 10th centile) with that of the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG)‐endorsed Delphi consensus criteria for late FGR for delivery of a small‐for‐gestational‐age (SGA) infant at term, emergency Cesarean section (CS) for non‐reassuring fetal status (NRFS), perinatal mortality and composite severe neonatal morbidity.

Methods

We classified retrospectively non‐anomalous singleton infants as having late FGR (diagnosed ≥ 32 weeks) according to SMFM and ISUOG/Delphi criteria in a cohort of women who had been referred to the Mater Mother's Hospital, Brisbane, Australia and who delivered at term between January 2014 and December 2020. The study outcomes were delivery of a SGA infant (birth weight (BW) < 10th or < 3rd centile), emergency CS for NRFS, perinatal mortality (defined as stillbirth or neonatal death within 28 days of a live birth) and a composite of severe neonatal morbidity. We assessed the screening performance of various ultrasound variables by calculating the sensitivity, specificity, positive (PPV) and negative (NPV) predictive values, false‐positive and false‐negative rates, positive likelihood ratio (LR+) and negative likelihood ratio.

Results

The SMFM and ISUOG/Delphi consensus criteria collectively classified 1030 cases as having late FGR. Of these, 400 cases were classified by both SMFM and ISUOG/Delphi criteria, whilst 548 cases were classified using only SMFM criteria and 82 cases were classified only by ISUOG/Delphi criteria. Prenatal detection of late FGR by SMFM and ISUOG/Delphi criteria was associated with increased odds of delivery of an infant with BW < 10th centile (SMFM: adjusted odds ratio (aOR), 133.0 (95% CI, 94.7–186.6); ISUOG/Delphi: aOR, 69.5 (95% CI, 49.1–98.2)) or BW < 3rd centile (SMFM: aOR, 348.7 (95% CI, 242.6–501.2); ISUOG/Delphi: aOR, 215.4 (95% CI, 148.4–312.7)). Compared with the SMFM criteria, the ISUOG/Delphi criteria were associated with lower odds (aOR, 0.5 (95% CI, 0.3–0.8)) of predicting a SGA infant with BW < 10th centile, but higher odds of predicting emergency CS for NRFS (aOR, 2.30 (95% CI, 1.14–4.66)) and composite neonatal morbidity (aOR, 1.22 (95% CI, 1.05–1.41)). Both SMFM and ISUOG/Delphi criteria were associated with high LR+, specificity, PPV and NPV for the prediction of infants with BW < 10th and BW < 3rd centile. However, both methods functioned much less efficiently for the prediction of composite severe neonatal morbidity or emergency CS for NRFS, with LR+ < 10. The SMFM biometric criteria alone, particularly AC < 3rd centile, had the highest LR+ values for the prediction of perinatal mortality.

Conclusion

Both the SMFM and ISUOG/Delphi criteria had strong screening potential for the detection of infants with BW < 10th or < 3rd centile but not for adverse neonatal outcome. © 2022 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.