1991 Volume 43 Issue 1 Pages 11-17
The umbilical artery, the fetal descending aorta and the fetal middle cerebral artery were examined by Doppler flow velocimetry for a total of 125 times in 109 normal pregnant women who ranged from the 24th to 41 st gestational week. Then a pulsatility index (PI) and a resistance index (RI) were calculated from blood flow velocity waveforms in each vessel. Moreover, we calculated the ratio of the descending aorta to the middle cerebral artery (DA/MCAratio) and the ratio of the umbilical artery to the middle cerebral artery (UA/MCAratio) for each index for further evaluation of fetal circulation. In the statistical evaluations, an unpaired t-test was used for comparisons.
As far as the umbilical artery was concerned, PI declined from 1.23±0.13 (mean±SD) to 0.88 ±0.13 (p< 0.001) from the 24th to the 33rd week, and after the 34th gestational week, kept almost the same value. RI of the umbilical artery also showed the same pattern as PI ; that is, it decreased from 0.699±0.039 to 0.585±0.062 (p <0.001) from the 24th to the 33rd week and no remarkable changes were observed after the 34th week of gestation.
No remarkable changes were observed in PI and RI of the fetal descending aorta through the pregnancy course after the 24th week, while indices in the fetal middle cerebral artery showed more complex changes. From the 24th to 29th gestational week, both PI and RI values increased from 2.29 ± 0.30 to 2.34±0.40, and 0.863 ±0.058 to 0.904±0.072, while they continuously decreased thereafter to 1.26 ±0.25, 0.655 ± 0.070 (p<0.001) at the 40th-41st weeks of gestation respectively.
DA/MCA ratios of PI increased from 0.765±0.050 to 1.076±0.236 (p < 0.001) from the 24th to 41 st gestational week. DA/MCA ratios of RI declined slightly from 0.943±0.054 to 0.911±0.077 from the 24th to 29th week, while thereafter they increased linealy up to 1.261 ±0.139 (p<0.001) at the 41 st week of gestation. UA/MCA ratios of PI and RI decreased until the 33rd week of gestation, and they turned to increase after the 34th week.
These findings suggest that changes in the fetal circulation and blood flow distribution reflect closely fetal physiological growth. Hence, such factors as fetal acidosis or insufficient feto-placental circulation and/or fetal growth retardation may be detected by means of Doppler flow velocimetry.
