Association of placental perfusion, as assessed by magnetic resonance imaging and uterine artery Doppler ultrasound, and its relationship to pregnancy outcome.

PURPOSE: To investigate (a) if placental perfusion in the second trimester of pregnancy, measured by two non-invasive magnetic resonance imaging (MRI) techniques, is related to impedance to flow in the uterine arteries, as assessed by Doppler ultrasound; and (b) if these measures are associated with future gestational outcome. METHODS: In 37 singleton pregnancies at 24-29 weeks' gestation, uterine artery pulsatility index (PI) was measured by Doppler ultrasound and placental perfusion was measured by Arterial Spin Labelling (flow-sensitive alternating inversion recovery (FAIR)) and intravoxel incoherent motion (IVIM) echo-planar imaging at 1.5 T in basal, central and placental regions of interest. The values were compared between those delivering small for gestational age (SGA) and appropriate for gestational age (AGA) neonates. RESULTS: In 23 pregnancies that resulted in delivery of SGA neonates, compared to the 14 with AGA neonates, the median basal FAIR measure was significantly lower (923.0 vs. 2359.0 arbitrary units; p = 0.003) as were IVIM measures of perfusing fraction (f) in basal, central and whole-placental regions (37.8 vs. 40.7%; p = 0.046; 24.3 vs. 35.1%; p = 0.014 and 27.9% vs. 36.2%; p = 0.001, respectively). In the SGA group, the median uterine artery PI was increased (1.96 vs. 1.03; p = 0.001). There were significant associations between uterine artery PI and placental perfusion assessed by both FAIR and IVIM. CONCLUSION: Pregnancies that result in SGA neonates exhibited reduced placental perfusion as assessed by MRI during the second trimester. This measurement was found to be strongly associated with impedance to flow in the uterine arteries. We suggest that FAIR or IVIM MRI examinations may be used to directly and non-invasively determine placental perfusion, and that the measured values are strong indicators of future gestational outcome.

Association of placental T2 relaxation times and uterine artery Doppler ultrasound measures of placental blood flow.

PURPOSE: To investigate whether, in the second trimester of pregnancy, placental T2 relaxation time (determined using magnetic resonance imaging (MRI)) is related to impedance to flow in the uterine arteries. METHODS: In 40 singleton pregnancies at 24-29 weeks' gestation, uterine artery pulsatility index (PI) was measured by Doppler ultrasound and T2 relaxation time was measured by echo planar MRI at 1.5 T. The significance of the associations between T2 relaxation time, uterine artery PI and birth weight were examined. RESULTS: In 25 pregnancies that delivered small for gestational age (SGA) neonates with birth weight below the 10th percentile, compared to those with appropriate for gestational age (AGA) birth weight, the T2 relaxation time was significantly decreased (88 ms vs. 149 ms, p < 0.0001) and uterine artery PI was increased (1.96 vs. 1.00, p < 0.0001). There were significant associations between placental T2 relaxation time and log10 uterine artery PI (r = -0.749, p < 0.0001), and between T2 relaxation and birth weight percentile (r = 0.693, p < 0.0001). CONCLUSION: The T2 relaxation time during the second trimester is shorter in pregnancies that subsequently deliver SGA neonates and the measurement is strongly correlated with impedance to flow in the uterine arteries.