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To investigate if placental volume in the second trimester of pregnancy is related to uterine artery blood flow and neonatal birth weight.In 83 singleton pregnancies at 24–29 weeks' gestation, uterine artery pulsatility index (PI) was measured by Doppler ultrasound and placental volume was calculated from images obtained by magnetic resonance imaging (MRI) at 1.5T. The significance of the association between placental volume, uterine artery PI, and birth weight was examined.In 37 normal pregnancies resulting in delivery of neonates with birth weight at or above the 10th percentile, the median placental volume increased with gestational age from 363 cm3 at 24 weeks to 515 cm3 at 29 weeks. In 46 pregnancies that resulted in delivery of small for gestational age (SGA) neonates with birth weight below the 10th percentile the median placental volume, corrected for gestational age, was significantly decreased by 120 cm3 (P < 0.0001) and median uterine artery PI was increased (1.87 vs. 1.59, P < 0.0001). There were significant associations between placental volume and both uterine artery PI (r = −0.677, P < 0.0001) and birth weight percentile (r = 0.658, P < 0.0001).Placental volume during the second trimester is smaller in pregnancies that subsequently deliver SGA neonates and the measurement is related to placental perfusion. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.