Perineal swelling during pregnancy in common chimpanzees and puerperal pathology

Perineal swelling during pregnancy in captive common chimpanzees (Pan troglodytes) was studied to examine if the swelling pattern is consistent with known fluctuations in estrogens and progesterone and to test associations between reduced swelling and pathological outcome. Analyses of swelling during 107 pregnancies with a variety of outcomes revealed that a majority of swelling patterns fit an endocrinological model closely, but that a small minority (6.6%) from low parity mothers had exaggerated and extended swelling, suggesting an altered sensitivity of the swelling to steroids. Disregarding this extreme minority, swelling was found to be significantly reduced from that of normal outcome pregnancies for sub-groups with varying degrees of maternal incompetence, neonatal fatality, and stillbirth. This reduction was most marked for pregnancies in nursery-reared mothers. Given the validity of the correspondence between swelling patterns and steroid concentrations, lower estrogen concentrations are implicated in the etiology of the puerperal pathologies seen. That steroid hormone concentrations during pregnancy may influence maternal behavior in apes provides a clue to the etiology of post-partum depression in women.