Maternal and fetal blood flow velocity waveforms in patients with preterm labor: prediction of successful tocolysis

Umbilical and uterine artery velocimetry was performed using continuous-wave Doppler ultrasound (Angioscan III) in 60 patients in preterm labor. Peak-systolic/end-diastolic ratios were calculated according to previously described techniques. All measurements were made before tocolytic therapy was begun: magnesium sulfate (n = 40) or ritodrine (n = 20). The mean gestational age was 33.1 +/- 1.5 weeks (range 29 to 36 weeks). Twelve (20%) patients had elevated (greater than 2.6) pretherapy uterine peak-systolic/end-diastolic ratios, 10 (16.7%) patients had elevated (greater than 3.5) pretherapy umbilical peak-systolic/end-diastolic ratios, and in eight (13.3%) patients both ratios were elevated. In seven (58.4%) of the 12 patients with elevated uterine peak-systolic/end-diastolic ratios, six (60%) of the 10 patients with elevated umbilical peak-systolic/end-diastolic ratios, and five (62.5%) of the eight patients with both ratios elevated tocolytics failed and the women were delivered within 48 hours, compared with seven (14.6%) of 48, eight (16%) of 50, and six (13.0%) of 46 with normal ratios, respectively (p less than 0.05). We conclude that patients in preterm labor with elevated pretherapy uterine and/or umbilical peak-systolic/end-diastolic ratios are more likely to fail tocolysis therapy and be delivered preterm than those with normal ratios. It may therefore be useful to include umbilical and uterine velocimetry in the initial evaluation of preterm labor.