Neonatal Anthropometric Measurements: A Comparison of Neonates With 3-T Fetal MRI Exposure, With 1.5-T Fetal MRI Exposure, and Without In-Utero MRI Exposure.

Background: Fetal MRI is increasingly performed at 3 T. Nonetheless, safety concerns persist regarding potential increased risk of intrauterine growth restriction from in-utero 3-T MRI exposure. Objective: To compare neonatal anthropometric measurements between newborns who underwent 3-T fetal MRI, newborns who underwent 1.5-T fetal MRI, and newborns without in utero MRI exposure. Methods: This single-center retrospective study included gravid patients who underwent fetal ultrasound and possible 1.5-T or 3-T fetal MRI within 10 days from January 2017 to January 2022. For each included patient who also underwent 3-T fetal MRI, one matched patient who also underwent 1.5-T MRI and two matched patients without in-utero MRI exposure, were randomly selected. Matching was based on gestational age per the fetal ultrasound. Neonatal anthropometric characteristics were compared among groups. Results: The final sample included 416 patients (mean age, 32±5 years), 104 in the 3-T MRI group, 104 in the 1.5-T MRI group, and 208 in the MRI-unexposed group. Mean gestational age at the time of fetal ultrasound used for matching was 27 weeks 2 days in the 3-T group, 25 weeks 2 days in the 1.5-T group, and 26 weeks 0 days in the MRI-unexposed group (p=.07). The distribution of indications for fetal MRI was not significantly different between the 3-T and 1.5-T groups (p=.62). Mean gestational age at delivery was 37 weeks 5 days in the 3-T group, 38 weeks 0 day in the 1.5-T group, and 38 weeks 2 days in the unexposed group (p=.51). No significant difference (p=.09) was observed among groups in mean neonatal weight (3-T: 3120±753 g; 1.5-T: 3104±704 g; unexposed: 2967±614 g); neonatal weight percentile (3-T: 45±27; 1.5-T: 42±26; MRI: 41±24); neonatal head circumference (3-T: 34±3 cm; 1.5-T: 34±3 cm; unexposed: 34±2 cm), or neonatal head circumference percentile (3-T: 48±29; 1.5-T: 42±23; unexposed: 43±30). Conclusion: There were no significant differences in neonatal anthropometric measurements among newborns who underwent in-utero 3-T MRI, newborns who underwent in-utero 1.5-T MRI, and newborns without in-utero MRI exposure. Clinical Impact: The results support the safety of 3-T MRI with respect to growth of the developing fetus.