Induction of parturition in pigs: short term effects of prostaglandin F2 alpha on chronically catheterised fetuses at term.

Blood pH and PaO2, and plasma glucose and cortisol concentrations were measured, together with myometrial electromyographic (EMG) activity and fetal heart rate, in eight chronically catheterised gilts and 13 of their fetuses during the induction of parturition with prostaglandin F2 alpha (given as the tromethamine salt). Myometrial EMG activity increased markedly in the first one to two hours after the injection but there was a period of relative quiescence over the next two to three hours. Fetal PaO2 fell significantly after the injection of PGF2 alpha (26.3 vs 21.8 Torr, P less than 0.001) but was unaffected by the injection of saline. Fetal and maternal cortisol concentrations increased significantly (fetal 57.3 vs 92.0 ng/ml, P less than 0.01; maternal 43.1 vs 84.9 ng/ml, P less than 0.001) in response to PGF2 alpha injection. Maternal PaO2 and fetal and maternal pH and plasma glucose concentrations were not altered by the injection of either prostaglandin PGF2 alpha or saline. Mean fetal heart rate increased by 7 to 10 per cent during the first hour after induction but this increase was not significant owing to the wide variations in response. It was concluded that the induction of parturition with prostaglandin F2 alpha resulted in a significant decrease in fetal oxygenation during the period of increased uterine activity but that this effect was transient and would not have an adverse effect in normal pregnancies.