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.