Risk Factors for Dystocia in Pigtailed Macaques (Macaca nemestrina)

Dystocia (difficult labor) is an important component of the management of nonhuman primates and results in significant fetal and maternal morbidity and increased use of veterinary resources. Dystocias can arise from abnormalities of the maternal pelvis or fetus or uncoordinated uterine activity. Although risk factors for stillbirths have been established in nonhuman primates, risk factors for dystocias have not. The objective of this study was to determine maternal and fetal risk factors for dystocia in macaques. Retrospective data were collected from 83 pigtailed macaques (Macaca nemestrina) diagnosed with dystocia. The diagnosis of dystocia was made based on clinical or pathologic evidence. Maternal records of age, reproductive history, experimental history, clinical records, and fetal birth weight and any applicable fetal necropsy reports were reviewed. The gestational age of the fetus, the infant's birth weight, total previous births by the dam, and the proportions of both viable delivery (inverse effect) and surgical pregnancy interventions (direct effect) in the dam's history generated a model that maximized the experimental variance for predicting dystocia in the current pregnancy and explained 24% of the dystocia deliveries. The number of total previous births and proportion of previous cesarean sections accounted for the greatest effect. This model can identify individual dams within a colony that are at risk for dystocias and allow for changes in breeding colony management, more intense monitoring of dams at risk, or allocation of additional resources.