Parturition in Macaca nemestrina

Measures were taken on 187 pregnancies of 104 pig‐tailed macaques ( Macaca nemestrina ) to document the normative course of parturition and to identify factors correlated with high risk for poor pregnancy outcomes. Analyses involved weekly physical examinations and diurnal sleep‐wake‐fulness patterns during trimester three; behavior during labor and delivery; and newborn sex, Apgar ratings, birthweight, and reflexes. Onset of labor was estimated at three–four hours before delivery, the time when circadian activity level first deviated from its predelivery pattern. Active labor averaged 92 minutes, and was characterized by increased uterine contractions and manipulation of the vaginal area. The modal delivery time was 2200 hr through 2400 hr. Most infants emerged from the vulva in a cranial‐anterior‐anterior presentation, with only a brief pause between head expulsion and complete emergence. Females with histories of poor pregnancy outcomes were more likely to deliver after midnight and showed less labor‐unique behavior than females with good outcome histories. Infants of high‐risk females that were delivered after midnight had lower Apgar scores and more bruising than infants of low‐risk females delevered before of after midnight, suggesting that high‐risk females may have more difficult deliveries. Overall, the results show that simple direct observations of parturition can yield important quantitative normative information that is correlated with reproductive risk factors.