Key result
Uterochorionic vascular resistance gradually decreased during the first trimester, with significant differences in velocimetry indices before versus after the 9th week of pregnancy.
Observational (n=25)
Pulsed Doppler velocimetry demonstrates a significant decrease in uterochorionic vascular resistance after the 9th week of normal pregnancy.
Establishes normative first-trimester Doppler trends; leaves open whether deviations predict placental disorders.
The natural course of uterochorionic vascular resistance during the first trimester of pregnancy is described. We performed a weekly study using a pulsed Doppler in 25 normal pregnancies, with a total of 191 examinations made. The flow velocity waveform was studied simultaneously in the retrochorionic area as well as in the uterine arteries. Different velocimetry indices were analysed, which demonstrated the feasibility of the (D/S) x 100 index for study of the retrochorionic vessels and of the Pourcelot index (S-D/S) for the uterine arteries. A gradual weekly decrease in flow resistance was found, with significant differences before [(D/S) x 100 = 52.01 +/- 8.33; S-D/S = 0.83 +/- 0.09] vs after the 9th week [(D/S) x 100 = 58.9 +/- 8.78; S-D/S = 0.72 +/- 0.10]. Further evaluation of its predictive and diagnostic value in gestational pathology is necessary.
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Mercé et al. (1989) conducted an observational in Normal pregnancy (n=25). Gestational age (after 9th week) vs. Before 9th week was evaluated on Flow resistance (velocimetry indices). Uterochorionic vascular resistance gradually decreased during the first trimester, with significant differences in velocimetry indices before versus after the 9th week of pregnancy.
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