Umbilical artery Doppler velocimetry in pregnancies of less than 21 weeks' duration.

Most Doppler ultrasound investigations of the umbilical artery circulation have been confined to beyond 16 weeks' gestation. The purpose of this study is to explore the evolution of this circulation in human pregnancies of less than 21 weeks' gestation. We studied 169 low-risk pregnant women (125 longitudinally and 44 cross-sectionally) with a pulsed Doppler system on 357 separate occasions between 9 and 20 weeks of gestation. Systolic/diastolic (S/D) ratios were used for waveform analysis. We obtained umbilical waveforms as early as 9 weeks. Before 13 weeks, all fetuses had absent end-diastolic velocity (AEDV), then progressive development of end-diastolic velocity (EDV) appeared from 13 to 18 weeks. At 18 weeks, all fetuses had developed EDV. S/D ratios progressively declined from 13 to 20 weeks (y = 17.67 - 1.26x + 0.3x2; r2 = .95). A cross-sectional evaluation of fetal heart rate in 136 fetuses revealed a significant negative second-order polynomial relationship with gestational age between 9 and 20 weeks y = 245.84 - 10.33x + 0.27x2; r2 = .93). In 136 fetuses, 185 measurements of S/D ratios and their corresponding fetal heart rate revealed no relationship (weighted linear regression, r2 = .005). Mean fetal heart rate was significantly higher when EDV was absent (164.6 +/- 10.8 standard deviation [SD], n = 74) than when EDV was present (150.1 +/- 5.8 SD; n = 62; P = .000). Thus, upstream factors may be of little importance in the generation of umbilical artery velocity waveforms in early pregnancy. Umbilical Doppler velocimetry in the first half of pregnancy gives a functional assessment of the vascular development of the umbilical-placental circulation.(ABSTRACT TRUNCATED AT 250 WORDS)