Color Doppler sonographic assessment of placental circulation in the first trimester of normal pregnancy.

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Our aim was to study placental circulation during the first trimester of normal pregnancy. For this purpose, 108 single pregnancies from 4 to 15 gestational weeks were evaluated through conventional Doppler ultrasonography. The flow velocity waveforms from the retrochorionic arteries (spiral-radial arteries) and the umbilical artery were assessed using the peak systolic velocity, resistive index, and pulsatility index). Intervillous flow velocity waveform was evaluated from the maximum velocity. The earliest color signal from the retrochorionic circulation was registered at 4.5 weeks along with gestational sac visualization. The venous Doppler signal from the intervillous space and the Doppler signal from the umbilical artery were recorded with an embryo visible from the end of week 5 onward. The retrochorionic, intervillous, and umbilical peak systolic velocities increase, whereas the resistive and pulsatility indices decrease progressively during early pregnancy with a significant correlation with gestational age. Similarly, intervillous maximum velocity gradually increases throughout the first trimester of pregnancy. Despite some methodologic problems related to Doppler technology and the vessels studied color Doppler sonography appears to be an adequate tool to assess the physiologic changes in the placental circulation during early pregnancy.