Changes in fetal supraventricular extrasystoles during uterine contractions in labour

The electrocardiogram and phonocardiogram were recorded from a fetus exhibiting supraventricular ectopic beats during labour. The ectopic beats showed increased amplitude of the first heart sound (S1) compared to sinus and postectopic beats; the R-S1 interval was prolonged and the mechanical systole, measured as the S1-S2 interval, shortened. During uterine contractions these parameters were measured every 10 sec. The S1 amplitude of the ectopic beats decreased; simultaneously the R-S1 interval increased and the S1-S2 interval shortened. The changes were delayed compared to the amniotic pressure curve. The changes found can be explained by a shift of blood between the fetus and placenta, caused by uterine contraction.