Pregnancy in systemic lupus erythematosus (SLE) is at high risk to the mother and fetus. Impaired utero-placental perfusion may increase fetal loss and intrauterine growth retardation. We assessed the changes in impedance to blood flow in the umbilical and uterine arteries in five patients with SLE treated with low dose aspirin and corticosteroids, using Doppler ultrasound longitudinally throughout pregnancy. Blood flow velocity waveforms of the umbilical and uterine arteries were studied by transabdominal and transvaginal Doppler ultrasound, respectively. Resistance index (RI) was measured every two to four weeks from week 10 to term, and the values obtained were compared to those of normal pregnancies. All five patients delivered uneventfully. One neonate was delivered at 36 weeks (2550 g) and one neonate was growth retarded (1900 g at 38 weeks). Three women delivered at 39 weeks (3585 g, 2850 g, and 2800 g). Most umbilical artery RI values obtained throughout pregnancy were above the 95th percentile of normal pregnancies. The highest values of RI of the umbilical artery were assessed in the case of fetal growth retardation. However, most measurements of RI of the uterine artery were under the 95th percentile of normal. The improved pregnancy outcome in patients with SLE treated with aspirin and corticosteroids seems to correlate with their normal uterine artery flow velocity wave forms.