Prediction of large‐for‐gestational age at 36 weeks' gestation: two‐dimensional ultrasound vs three‐dimensional ultrasound vs magnetic resonance imaging

ABSTRACT Objective To compare the performance of two‐dimensional ultrasound (2D‐US), three‐dimensional ultrasound (3D‐US) and magnetic resonance imaging (MRI) at 36 weeks' gestation in predicting the delivery of a large‐for‐gestational‐age (LGA) neonate, defined as birth weight ≥ 95 th percentile, in patients at high and low risk for macrosomia. Methods This was a secondary analysis of a prospective observational study conducted between January 2017 and February 2019. Women with a singleton pregnancy at 36 weeks' gestation underwent 2D‐US, 3D‐US and MRI within 15 min for estimation of fetal weight. Weight estimations and birth weight were plotted on a growth curve to obtain percentiles for comparison. Participants were considered high risk if they had at least one of the following risk factors: diabetes mellitus, estimated fetal weight ≥ 90 th percentile at the routine third‐trimester ultrasound examination, obesity (prepregnancy body mass index ≥ 30 kg/m 2 ) or excessive weight gain during pregnancy. The outcome was the diagnostic performance of each modality in the prediction of birth weight ≥ 95 th percentile, expressed as the area under the receiver‐operating‐characteristics curve (AUC), sensitivity, specificity and positive and negative predictive values. Results A total of 965 women were included, of whom 533 (55.23%) were high risk and 432 (44.77%) were low risk. In the low‐risk group, the AUCs for birth weight ≥ 95 th percentile were 0.982 for MRI, 0.964 for 2D‐US and 0.962 for 3D‐US; pairwise comparisons were non‐significant. In the high‐risk group, the AUCs were 0.959 for MRI, 0.909 for 2D‐US and 0.894 for 3D‐US. A statistically significant difference was noted between MRI and both 2D‐US ( P = 0.002) and 3D‐US ( P = 0.002), but not between 2D‐US and 3D‐US ( P = 0.503). In the high‐risk group, MRI had the highest sensitivity (65.79%) compared with 2D‐US (36.84%, P = 0.002) and 3D‐US (21.05%, P < 0.001), whereas 3D‐US had the highest specificity (98.99%) compared with 2D‐US (96.77%, P = 0.005) and MRI (96.97%, P = 0.004). Conclusions At 36 weeks' gestation, MRI has better performance compared with 2D‐US and 3D‐US in predicting birth weight ≥ 95 th percentile in patients at high risk for macrosomia, whereas the performance of 2D‐US and 3D‐US is comparable. For low‐risk patients, the three modalities perform similarly. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.