Placental T2* and BOLD effect in response to hyperoxia in normal and growth-restricted pregnancies: multicenter cohort study.

Objectives: Blood-oxygen-level-dependent (BOLD) magnetic resonance imaging (MRI) facilitates the non-invasive in-vivo evaluation of placental oxygenation. The aims of this study were to identify and quantify a relative BOLD effect in response to hyperoxia in the human placenta and to compare it between pregnancies with and those without fetal growth restriction (FGR).

Methods: This was a prospective multicenter study (NCT02238301) of 19 pregnancies with FGR (estimated fetal weight (EFW) on ultrasound < 5 centile) and 75 non-FGR pregnancies (controls) recruited at two centers in Paris, France. Using a 1.5-Tesla MRI system, the same multi-echo gradient-recalled echo (GRE) sequences were performed at both centers to obtain placental T2* values at baseline and in hyperoxic conditions. The relative BOLD effect was calculated according to the equation 100 × (hyperoxic T2* - baseline T2*)/baseline T2*. Baseline T2* values and relative BOLD effect were compared according to EFW (FGR vs non-FGR), presence/absence of Doppler anomalies and birth weight (small-for-gestational age (SGA) vs non-SGA).

Results: We observed a relative BOLD effect in response to hyperoxia in the human placenta (median, 33.8% (interquartile range (IQR), 22.5-48.0%)). The relative BOLD effect did not differ significantly between pregnancies with and those without FGR (median, 34.4% (IQR, 24.1-48.5%) vs 33.7% (22.7-47.4%); P = 0.95). Baseline T2* Z-score adjusted for gestational age at MRI was significantly lower in FGR pregnancies compared with non-FGR pregnancies (median, -1.27 (IQR, -4.87 to -0.10) vs 0.33 (IQR, -0.81 to 1.02); P = 0.001). Baseline T2* Z-score was also significantly lower in those pregnancies that subsequently delivered a SGA neonate (n = 23) compared with those that delivered a non-SGA neonate (n = 62) (median, -0.75 (IQR, -3.48 to 0.29) vs 0.35 (IQR, -0.79 to 1.05); P = 0.01).

Conclusions: Our study confirms a BOLD effect in the human placenta and that baseline T2* values are significantly lower in pregnancies with FGR. Further studies are needed to evaluate whether such parameters may detect placental insufficiency before it has a clinical impact on fetal growth. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.