Breathing movements before death in the primate fetus (Macaca mulatta)

The incidence and character of fetal breathing movements (FBMs) were determined by analysis of continuous tracheal pressure recordings in a 48 hour period preceeding fetal death in utero in 7 chronic pregnant monkey preparations (Macaca mulatta). All fetuses were judged normal by blood gas tensions, pH, and fetal heart rate within 48 hours of death. In the normal fetus breathing movements were periodic and a circadian distribution in the incidence of FBMs was observed. Four distinct patterns of FBMs were observed in the normal fetuses. In five fetuses death occurred in the intrapartum period; all five fetuses were breathing at the onset of labor. A progressive fall in the incidence of FBMs was observed in labor coincident with the development of fetal acidemia. In the remaining two fetuses death occurred before labor. Apnea and gasping were observed in all fetuses before death. The duration of apnea and gasping appeared dependent upon the nature of the lethal insult.