ABSTRACT: Fetal heart rate patterns, and intrauterine and maternal blood pressures were recorded during various types of maternal bearing-down efforts. Bearing-down efforts which lasted more than 5 seconds resulted in late decelerations of the fetal heart rate, marked falls in the maternal systolic and diastolic blood pressures and resultant delayed recovery of the fetal heart rate, with fetal hypoxia and acidosis in some cases. When women are not urged to bear down long and hard, their spontaneous efforts are usually within physiologic limits-5–6 seconds long-and fetal acidosis is thereby avoided.