Alteration of FHR pattern associated with progressively advanced fetal acidemia caused by cord compression

In order to investigate changes in FHR when a fetus suffers acidemia, we produced progressively advanced acidemia in lamb fetus by intermittently repeated cord compression. FHR was monitored throughout the study. FHR patterns were classified into five characteristic types as fetal arterial pH fell from around 7.35 to below 6.90. It was confirmed by studies involving catecholamine release and the administration of drugs such as atropine sulfate, alpha or beta adrenergic antagonists that sympathetic and parasympathetic regulation was deeply involved in the changes. Among the patterns, type 4, in which decreased amplitude of the initial drop and hypoxia-induced deceleration was followed by overshoot acceleration, took place during acidemia at arterial pH below 7.15. In conclusion, the appearance of type 4 FHR indicates a deteriorating state in human fetus as well, induced by repeated cord compression, and obliges us to deliver the fetus as soon as possible.