Placental magnetic resonance imaging T2* measurements in normal pregnancies and in those complicated by fetal growth restriction

OBJECTIVES: The Magnetic Resonance Imaging (MRI) variable T2* depends on multiple factors. One important factor is the presence of deoxyhemoglobin. We aimed to describe placental T2* in normal pregnancies and in pregnancies with fetal growth restriction (FGR).

METHODS: We included 24 normal pregnancies (gestational week 24-40) and four FGR cases with estimated fetal weight below the 1(st) centile. Prior to the MRI, an ultrasound examination including Doppler flow measurements was performed. Placental histological examination was made in the FGR cases. The T2* value was calculated using a gradient echo sequence with readout at 16 echo times. In the normal pregnancies, repeat T2* measurements and inter-observer reproducibility were assessed in order to estimate the reproducibility of the method.

RESULTS: The method was robust regarding the technical - and the inter-observer reproducibility. However, some slice to slice variation existed due to the heterogeneous nature of the normal placenta. We therefore based the T2*-estimations on the average of two slices from each placenta. In the normal pregnancies, the placental T2* value decreased significantly with gestational age being 120 ± 17 ms (mean, SD) in week 24, 84 ± 16 ms in week 32, and 47 ± 17 ms in week 40. Three FGR cases had abnormal Doppler flows, histological signs of maternal hypoperfusion and a reduced T2* value (Z-scores < -3.5). In the fourth FGR case, Doppler flows, placental histology and T2* value (Z-score -0.34) were normal.

CONCLUSIONS: The established reference values for placental T2* may be clinically useful as the T2* values were significantly reduced in FGR-cases with histological signs of maternal hypoperfusion.