['To evaluate the influence of uterine artery impedance to blood flow on the day of embryo transfer for prediction of early pregnancy loss and obstetric outcome.', 'The uterine artery pulsatility index (PI) and resistance index (RI) were evaluated prospectively by transvaginal Doppler in 102 infertile women, who conceived as the result of fresh or frozen embryo transfer. Uterine artery impedance to blood flow was compared to the obstetric outcome.', 'The 111 treatment cycles studied resulted in 31 spontaneous abortions, four ectopic pregnancies, and 76 deliveries. There were no differences in uterine artery PI and RI (mean +/- SD) between cycles resulting in normal delivery (2.69 +/- 0.71 and 0.88 +/- 0.06) and those resulting in spontaneous abortion (2.71 +/- 0.67 and 0.88 +/- 0.05) or ectopic pregnancy (2.36 +/- 0.54 and 0.85 +/- 0.06). There were no differences in PI and RI between uncomplicated singleton pregnancies (2.74 +/- 0.78 and 0.88 +/- 0.06) and those developing intra-uterine growth restriction (IUGR), pregnancy-induced hypertension (PIH), or preterm birth (2.54 +/- 0.47 and 0.87 +/- 0.04, pooled data).'] Does uterine artery impedance to blood flow on the day of embryo transfer predict obstetric outcome?