Combined use of beta-sympathomimetic drugs and beta-blockers during labour.

None of the betamimetics have a exclusively tocolytic effect. By stimulating the cardiovascular beta-receptor, they also cause a substantial increase in the heart rate and a decrease in blood pressure. We administered 4--5 micrograms/min of Fenoterol to 13 patients during the first stage of labour. This led to complete inhibition of labour. To reduce cardiac side effects, a primarily cardiac beta-blocker (5 mg Atenolol or 20 mg Metoprolol) was also given. The maternal and fetal heart rates were measured by ECG and by fetal scalp-electrode, respectively. The fetal heart rate remained largely unchanged, both during the Fenoterol infusion as well as during the additional administration of the beta-blocker. The maternal heart rate, which increased under the influence of the Fenoterol, fell (p less than or equal to 0.01) but did not return to normal. In all cases the beta-blockade led to a brief increase in uterine activity.