[Ultrasound studies of blood flow in the umbilical vein].

The umbilical vein blood flow was examined in a total of 101 healthy pregnant women in 146 occasions between the 28th and 41st weeks of pregnancy. A Kranzbühler 8130 Duplex Doppler machine was used in all of the examinations. It was found that the blood flow is near to the same value (120 ml/min/kg) till the 37 to 38th weeks of pregnancy during the third trimester, then decreases continuously and is about 90 ml/min/kg on the 41st week of pregnancy. The diameter of the umbilical vein increases from 4-5 mm to 6-7 mm, but the rate of growth slows down after the 36-37th weeks. The velocity of the blood flow between the 28th and 41st weeks of pregnancy fluctuates between wide limits (10-24 cm/s), but a slight decrease could be observed from the 36-37 weeks of pregnancy.