Prenatal assessment of the Hyrtl anastomosis and evaluation of its function

The presence of a communicating vessel, the Hyrtl anastomosis, between the umbilical arteries is well described in pathological studies. Using different injection techniques, it has been speculated that this vessel acts as a pressure-equalizing mechanism between the different lobes of the placenta. However, its detection during fetal life has never been reported. We report on two cases of ultrasonographic detection and Doppler assessment of the Hyrtl anastomosis during pregnancy. A pulsatile blood how from the umbilical artery with higher resistance to that with lower resistance has been demonstrated at the level of the Hyrtl anastomosis, which was confirmed after delivery. In addition, this report supports the hypothesis that the anastomosis plays an important role in regulating the blood pressure in the placental lobes and in equalizing the blood pressure between umbilical arteries.