Lack of association between pelvic outlet diameter and pelvic organ prolapse in squirrel monkeys

Introduction and hypothesis: The aim was to test the hypothesis that the pelvic outlet diameter (POD) is associated with pelvic organ prolapse (POP) in squirrel monkeys. Methods: Magnetic resonance images (MRI) were obtained from 55 females with and without POP. Commercial software was used by two observers to measure the POD. POD, age, parity, and weight for the two groups were compared using Student's t test. Associations of age, parity, and body weight with POD were evaluated with linear regression analysis. Multiple regression analysis examined the relationships of age, parity, and POD with POP. Receiver operating curve methods were used to set thresholds. Results: Observers concurred on measurements (Cronbach's alpha=0.96 with lower 95 % confidence limit of 0.94). POD was not related to parity (p=0.10) or weight (p=0.053), but was inversely related to age (p=0.011). Animals with POP did not differ from those without POP with regard to age (p=0.10), weight (p=0.17), or POD (p=0.99). The groups differed with regard to parity (p=0.007) and multiple regression methods demonstrated that only parity had a significant relationship with POP (p=0.002). Parity greater than 2 had 64 % specificity and 89 % sensitivity for POP. Conclusions: POD size does not contribute to POP in squirrel monkeys. This study confirms that among variables of age, body weight, POD, and parity, only parity appears as a risk factor for POP in squirrel monkeys.