Fetal magnetic resonance imaging at 36 weeks predicts neonat
Large-for-gestational age (LGA) fetuses are at increased risk of perinatal morbidity and mortality. Prediction of macrosomia using magnetic resonance imaging (MRI) appears to be more accurate than ultrasound (US).

The objective was to prospectively compare estimates of fetal weight based on 2-dimensional US (US-EFW) and MR imaging (MR-EFW) to actual birth weight in routine antenatal populations.

In this prospective, single-center, blinded study, pregnant women with singleton pregnancies between 36+0 – 36+6 weeks gestation, underwent both standard evaluation of estimated fetal weight with the US and MRI, based on the measurement of the fetal body volume (FBV). Participants and clinicians were aware of the results of the US but blinded to the MRI estimates. Birth weight centile was considered as the gold standard for the US and MRI-derived centile.

The primary outcome was the area under the receiver-operating characteristic curve (AUROC) for the prediction of ≥ 95th centile LGA neonates. Secondary outcomes included the comparative prediction of LGA neonates ≥ 90th, 97th, 99th centile, small-for-gestational-age (SGA) ≤ 10th, 5th, 3rd centile for gestational age and maternal/perinatal complications.

Of 2,914 women who were initially approached, results from 2,378 were available for analysis. Total FBV measurements were possible for all fetuses and the time required to perform the planimetric measurements by MRI was 3.0 minutes.

- The AUROC curve for prediction of birthweight ≥ 95th centile by prenatal MRI was 0.985 and by the US it was 0.900.

- For a fixed false-positive rate of 5 %, MRI-EFW detected 80.0% whereas US-EFW detected 59.1% of birthweight ≥ 95th centile.

- The positive predictive value (PPV) was 42.6% for MRI-EFW and 35.4% for US-EFW, and the negative predictive value (NPV) was 99.0% for MRI-EFW and 98.0 for US-EFW.

- For a fixed false-positive rate of 10 %, MRI-EFW detected 92.4% whereas US-EFW detected 76.2% of birthweight ≥ 95th centile.

- The PPV was 29.9% for MRI-EFW and 26.2% for US-EFW and the NPV was 99.6 for MRI-EFW and 98.8 for US-EFW.

- The AUROC curves for prediction of LGA ≥ 90th, 97th, 99th centile, and SGA ≤ 10th, 5th, 3rd centile were significantly larger by prenatal MRI as compared to the US.

At the 36th week of gestation, MRI-EFW performs significantly better than US-EFW in the prediction of LGA ≥ 95th centile for gestational age, as well for all other recognized cut-offs of LGA and SGA.

American Journal of Obstetrics & Gynecology
Source: https://doi.org/10.1016/j.ajog.2021.08.001