Intervillous circulation in all three trimesters of normal pregnancy assessed by color Doppler

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Abstract
Our cross-sectional study included 115 healthy pregnant women in gestational age between 7 and 24 weeks. The aim of the study was to compare resistance (RI) and pulsatility (PI) indices, peak systolic velocity (PSV), end-diastolic velocity, and temporal averaged maximum velocity (TAMV) of the spiral arteries and vessels within the intervillous space in all three trimesters of pregnancy. The impedance to blood flow within the intervillous space significantly decreased towards the mid-pregnancy (p < 0.01) and then remained stable. Blood flow velocities within the intervillous space expressed by PSV, EDV and TAMV increased significantly (p < 0.01) towards the mid-pregnancy. After reaching the plateau between 16 and 22 weeks of gestation, these parameters remained almost constant until the 36th gestational week. Near the term low-significant decrease of blood flow velocities was noted: for PSV and TAMV p < 0.07, and for EDV p < 0.05. A significant increase in continuous intervillous blood flow velocity was noted from the 11th week onward (28 +/- 12 vs. 36 +/- 12) until the 36th week of gestation (36 +/- 12 cm/s). The first report of the haemodynamic changes within the intervillous space during pregnancy may have implication in better understanding of the metabolical interchange between maternal and fetal side.