Uterine Tachysystole, Hypertonus and Hyperstimulation: An Urgent Need to get the Definitions Right to Avoid Intrapartum Hypoxic-Ischemic Brain Injury

This is because fetal oxygenation and removal of metabolic waste products occurs predominantly during periods of uterine relaxation, when the maternal spiral arterioles and uterine venules feeding the placental venous sinuses are open and the blood vessels within the umbilical cord are not compressed. At rest, the pressure within the spiral arteries is greater than the intramyometrial pressure, resulting in blood flow into the intervillous space. The waste products exit through the low-pressure venous system into the maternal circulation. During a uterine contraction, the myometrial pressure exceeds the spiral arterial pressure, and the uterine blood flow is interrupted causing a cessation in oxygen delivery to the fetus. The duration of the spiral artery compression depends on the strength and the duration of the contraction. In a recent systematic review by Reynolds et al, an increased uterine activity was found to be a non-specific predictor of depressed