RESUMO
The umbilical artery flow is an important parameter for the management of obstetrical patients, specially those with retardation in intrauterine growth. A prospective study was carried out in 123 normal, pregnant women, from 20 to 40 weeks of gestation, with a reliable last menstruation date, who came for prenatal control to the Gyn-Ob Department at Hospital Central Militar, from June, 1991 to May 31, 1992. Umbilical artery velocimetry measurements, were done periodically, with S/D ratio determination, avoiding fetal respiratory movements, and at the chord site closest to the placenta. The equipment used was Toshiba Sonolayer SSA-270-A Doppler Duplex of pulsated wave; frequency of transmission-reception 3.5 Mhz and transductor fo 12 mm. diameter. All 123 products had a complete clinical examination, and determination of gestational age by Capurro at the time of birth, in order to exactly identify the gestational age of each ultrasonographic examination. With the obtained results four curves were made. One with average and standard error (EE +/- 1); another of simple lineal regression, obtaining confidence intervals of 95% with a correlation coefficient of r = 0.89; another one based on percentile 10, 50 and 90; and finally, one curve based of the confidence interval of 95%. The results are similar to the ones obtained by other authors, diminishing S/D ratio since week 20 to 40.