Umbilical and uterine artery flow velocity waveforms in normal pregnancy and pregnancy induced hypertension.

Umbilical and uterine artery Doppler studies were carried out in 113 cases of normal pregnancy and in 32 patients with pregnancy induced hypertension (PIH). The results were analyzed by calculating the systolic/diastolic (S/D) ratio. In normal pregnancy the umbilical velocity wave S/D ratio declined from 3.9 to 2.1 from 20th week to term, and the uterine wave S/D ratio remained constant between 1.8 and 1.9. In many cases of severe PIH the umbilical and uterine artery velocity wave S/D ratios were raised, indicating increased resistance to the blood flow. The changes of umbilical waveforms appeared earlier than those of the uterine arterial waveforms.