Early fetal MRI in the late first and early second trimester: a pictorial essay.

With the rapid development and nearly universal acceptance of first trimester nuchal translucency ultrasound, in conjunction with screening for common aneuploidies through maternal blood testing, fetal anomalies are increasingly identified between 10 weeks and 14 weeks of gestation. When anatomic findings on sonography at this gestational age are indeterminate, options for further imaging evaluation have been limited. Historically, fetal magnetic resonance imaging (MRI) has been deferred until 18 weeks to 20 weeks of gestation due to concerns about safety, small fetal size and fetal motion. Published studies thus far show no evidence indicating harm to the fetus from MRI exposure at any stage of pregnancy for field strengths at or below 3.0 tesla. Fetal MRI can provide detailed, high-resolution diagnostic images as early as 11 weeks of gestation, despite fetal motion or small fetal size. This article presents a small series of late first and early second trimester fetuses selected from a larger cohort referred to our center for anomalies seen or suspected on sonography. We present selected images from same-day fetal sonography and MRI performed in our center, highlight the information obtained from each modality, and discuss how the combined information obtained influenced maternal counseling and pregnancy outcome. Early fetal MRI requires real-time changes in routine imaging protocols, with frequent communication between the performing MRI technologist and the reading radiologist. The cases presented here suggest that early fetal MRI can be added to our imaging armamentarium and may assist patients and clinicians with earlier and more accurate diagnoses. In our experience, the information obtained from early fetal MRI often confirms or adds details to anomalies seen or suspected on sonography.