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Magnetic resonance imaging for prenatal estimation of birth weight in pregnancy

Journal Contribution - Review Article

Subtitle:review of available data, techniques, and future perspectives

Fetuses at the extremes of growth abnormalities carry a risk of perinatal morbidity and mortality. Their identification is traditionally done by 2-dimensional ultrasound, the performance of which is not always optimal. Magnetic resonance imaging (MRI) superbly depicts fetal anatomy and anomalies and has largely contributed to the evaluation of high-risk pregnancies. In 1994, Baker et al. introduced MRI for estimation of fetal weight (EFW). This is done by measuring the fetal body volume (FBV) and converting it through a formula to fetal weight. About 10 studies have shown that MRI is more accurate than 2-dimensional ultrasound in EFW. Yet, despite its promise, the MRI technique is not currently implemented clinically. Over the last 5 years, this technique has evolved quite rapidly. Here we review the literature data, provide details of the various measurement techniques and formulas, consider the application of MRI technique in specific populations such as diabetics and twin pregnancies, and conclude with what we believe could be the future perspectives and clinical application of this challenging technique. EFW by ultrasound is mainly based on the algorithm described by Hadlock et al. which takes into account the measurement of biparietal diameter, head circumference, abdominal circumference and femur length. EFW by MRI is based on the formula by Baker et al.: MRI-EFW in Kg = 1.031 x FBV (in Liters) + 0.12. or by Kacem et al.: MRI-EFW in g = 1.2083 x FBV (in mL)ˆ(0.9815). Comparison of these 2 formulas for the detection of large-for-gestational age neonates showed similar performance for preterm (P=0.479) and for term fetuses (P=1.000). Literature data show that EFW with MRI carries a mean or median relative error of 2.6 up to 3.7% when measurements were performed at < 1 week from delivery whereas for the same fetuses, the relative error at two-dimensional ultrasound varied between 6.3 and 11.4%. Further, in a series of 270 fetuses evaluated within 48 hours from birth, and for a fixed false positive rate of 10%, MRI detected 98% of large-for-gestational age neonates (≥ 95th centile for gestation) compared with 67% with ultrasound estimates. On the same series, MRI applied to the detection of small-for-gestational age neonates ≤ 10th centile for gestation, for a fixed 10% false positive rate, reached a detection rate of 100 % compared with only 78 % for ultrasound. Planimetric measurement has been one of the main limitations of MRI for EFW. Software programs allowing semi-automatic segmentation of the fetus are available from imaging manufacturers or are self-developed. We have shown that all perform equally well for the prediction of large-for-gestational age neonates, with the advantage of the semi-automatic methods being less time-consuming. Although many challenges remain for this technique to be generalized, a 2-step strategy following selection of a group at high risk of the extremes of growth abnormalities is the most likely scenario. Results of ongoing studies are awaited (ClinicalTrials.gov Identifier # NCT02713568).

Journal: American Journal of Obstetrics and Gynecology
ISSN: 0002-9378
Issue: 5
Volume: 220
Pages: 428-439
Publication year:2019
Keywords:EFW, Fetal weight, estimation of fetal weight, fetal biometry, agnetic resonance imaging, semi-automated software, wo-dimensional -ultrasound
CSS-citation score:2
Accessibility:Closed