Prediction of Low Birth Weight: Comparison of Placental T2* Estimated by MRI and Uterine Artery Pulsatility Index

Objective: Neonates at low birth weight due to placental dysfunction are at high risk of adverse outcomes. These outcomes can be substantially improved by prenatal identification. The Magnetic Resonance Imaging (MRI) constant, placental T2* reflects placental structure and oxygenation and thereby placental function. Therefore, we aimed to evaluate the performance of placental T2* in the prediction of low birth weight using the uterine artery (UtA) pulsatility index (PI) as gold standard.

Methods: This was a prospective observational study of 100 singleton pregnancies included at 20-40 weeks' gestation. Placental T2* was obtained using a gradient recalled multi-echo MRI sequence and UtA PI was measured using Doppler ultrasound. Placental pathological examination was performed in 57 of the pregnancies. Low birth weight was defined by a Z-score ≤ -2.0.

Results: The incidence of low birth weight was 15%. The median time interval between measurements and birth was 7.3 weeks (interquartile range 3.0, 13.7 weeks). Linear regression revealed significant associations between birth weight Z-score and both placental T2* Z-score (r = 0.68, p < 0.0001) and UtA PI Z-score (r = -0.43, p < 0.0001). Receiver operating characteristic curves demonstrated a significantly higher performance of T2* (AUC of 0.92; 95% CI, 0.85-0.98) than UtA PI (AUC of 0.74; 95% CI, 0.60-0.89) in the prediction of low birth weight (p = 0.010). Placental pathological findings were closely related to the T2* values.

Conclusions: In this population, placental T2* was a strong predictor of low birth weight and it performed significantly better than the UtA PI. Thus, placental T2* is a promising marker of placental dysfunction which deserves further investigation.