Charting normative reference values and Z-scores for MRI-derived in vivo placental growth

BACKGROUND: In vivo placental volume derived from magnetic resonance imaging (MRI) is a novel imaging tool to evaluate the placenta during pregnancy, as the placenta is difficult to access throughout gestation. There is a paucity of established standardized normative raw values and Z-scores for in vivo placental volume based on MRI. OBJECTIVE: To establish normative references for in vivo placental MRI-based volumes derived from a large cohort of healthy pregnant women carrying healthy fetuses throughout gestation. MATERIALS AND METHODS: Healthy pregnant women with healthy singleton pregnancies greater than 16 weeks gestation were enrolled in a longitudinal, prospective observational study. In total, 313 placental MRIs were analyzed from 209 pregnant women. In-vivo placentas were manually segmented to derive volumes and Z-scores. Means, standard deviations, and percentiles for normative reference raw values were calculated using weekly gestational age (GA) bins. Placental volume Z-scores were calculated based on 2-week GA bins using means and standard deviations. RESULTS: Normative reference placental volumes from 209 subjects (313 scans) with median GA 31.43 8.86 weeks are presented in weekly and bi-weekly GA bins. Using 2-week GA intervals, 95% of placental volume Z-scores were within ±2 standard deviations of the population mean. CONCLUSION: This data provides established normative in vivo raw and Z-score values derived from placental MRI. The value of accessing the placenta in vivo through MRI has become increasingly recognized, as the importance of the placenta in fetal and postnatal health is now more widely known. Establishing normative reference values for the in vivo placenta throughout gestation benefits both the clinical and scientific communities.