Normative ranges of MRI-based placental volume and placental-to-fetal-volume ratio at 16-36 weeks: prospective study

The placenta plays a crucial role in fetal development, yet normal placental volumetric growth trajectories remain poorly characterized, as most studies focus on pathological pregnancies or limited gestational-age (GA) ranges. We aimed to establish magnetic reference imaging (MRI)-based normative reference curves for placental volume (PV) and the placental-to-fetal-volume ratio (PFR) between 16 and 36 weeks' gestation.

This single-center, prospective study conducted as part of the 'LUMIERE on the Fetus' project included healthy pregnant women with a low-risk, singleton, 16-36-week fetus evaluated between December 2021 and June 2022. Additional participants with MRI data available at 16 weeks were recruited between January 2023 and October 2025. MRI was performed using a standardized protocol, and placental and fetal volumes were segmented using three-dimensional imaging software. Mean fetal body volume across 16-36 weeks was derived from our previously published normative MRI-based dataset obtained from the same cohort. Mean PV and PFR were calculated for each week of gestation. PV growth across gestation was modeled using logarithmic regression, while PFR growth was modeled using a quadratic term, and percentile curves were generated.

The study cohort comprised 265 MRI datasets from 247 healthy pregnant women with a singleton fetus. Mean PV increased from 149 cm³ at 16 weeks to 890 cm³ at 36 weeks, following the function: PV(GA) = (911.3 × ln(GA)) - 2375.7, where GA is in weeks. Over the same period, fetal body volume increased 22-fold, leading to a progressive decline in PFR. Specifically, mean PFR decreased from 1.22 at 16 weeks to 0.31 at 36 weeks, confirming its downward trajectory as fetal growth progresses. The relationship between PFR and GA was modeled using the quadratic function: PFR(GA) = 4.03 - (0.215 × GA) + (0.00313 × GA²), where GA is in weeks.

This study establishes MRI-based normative percentile curves for PV and PFR, from 16 to 36 weeks' gestation, confirming the physiological decline in PFR with advancing gestation. These benchmarks may aid in detecting placental dysfunction and characterizing fetal growth restriction. Further validation is needed in pathological and multiple pregnancies. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.