Chimpanzee births in captivity: a typical case history and report of sixteen births

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Abstract
Gestation periods of 13 captive chimpanzees in the Yale Laboratory of Primate Biology varied from 216 to 261 days (average, 236). Ovulation, determined by controlled matings, occurred at the midpoint of the cycle in [female][female] with a typical 35-day sexual cycle, a few days after the midpoint in [female][female] with longer cycles. Menstrual bleeding did not occur during pregnancy, though genital swelling was observed in the early stages. Labor was usually short, delivery sometimes occurring within 1 hr., with vertex presentation in all the observed cases. The afterbirth was expelled soon after the fetus. The [female] typically licked up the expelled amniotic fluids and sometimes ate the afterbirth. During pregnancy and nursing the [female][female] became gentle and more easily handled. Asehheim-Zondek and Friedman tests for pregnancy proved unreliable for chimpanzees.