Quantitative Mri Measures Of In Utero Feto-Placental Trajectories In Healthy Pregnancies

INTRODUCTION: The birth weight-placental weight ratio, a metric of placental efficiency in supporting fetal growth, is associated with fetal demise, neonatal and maternal morbidity. However, in vivo measures of placental health remain lacking. This study uses fetal body and placental volume metrics to (1) characterize in utero feto-placental growth patterns using in vivo three-dimensional MRI and (2) explore these associations with neonatal outcomes. METHODS: IRB approval was obtained. In a prospective observational study, healthy women with singleton pregnancies greater than 18 weeks gestation were recruited and underwent fetal MR imaging. The fetal body and placenta were manually outlined using ITK-SNAP software, volumes were calculated in mm3 and feto-placental ratio (FPR) was derived. Clinical data including gestational age (GA) at delivery, birthweight (BW) and corrected birthweight (BW z-score) were obtained. RESULTS: Thirty-five women underwent fetal MRI between 25 and 38 completed weeks gestation (mean=31.98±4.20). All pregnancies resulted in live births; 3 (8.5%) infants had birth weights less than 10% and 2 (5.7%) delivered before term. There was a positive association between GA and both fetal body volumes (FBV) and placental volumes (PV) (P<.001 for both) and between GA and FPR (P<.001). There was no association between in vivo FPR and GA at delivery or BW z-score, even with controlling for GA at MRI ( P= .12–.88). CONCLUSION: We describe in utero trajectories for fetal-placental growth in healthy pregnancies using quantitative MRI tools. Understanding normal patterns of fetal-placental development are needed to be able to detect early in utero placental failure prior to the onset of fetal harm.