Reproductive health assessments in female polar bears: Anatomy, pathology, and diagnostic techniques

Abstract

The reproductive success of polar bears (Ursus maritimus) in U.S. zoos is poor and the underlying causes of reproductive failure remain elusive. It is evident that new methodologies for evaluating fertility are needed, along with baseline information about species-specific reproductive anatomy and physiology. Between 2012 and 2024, 25 examinations of 17 female polar bears were conducted opportunistically, and included vulvar measurements, vaginal cytology, vaginoscopy, hysteroscopy with endometrial biopsy, and/or ultrasonography. Additionally, reproductive tracts (n = 10) harvested post-mortem were examined shortly after collection, allowing for inspection of anatomy ex vivo. The outcomes of these activities yielded detailed measurements and descriptions of reproductive anatomy. Vaginal cytology patterns demonstrated shifts in vaginal epithelial cell type associated with estrus and vaginoscopy enabled systematic evaluation of internal reproductive structures, including the vestibule, vestibulo-vaginal junction, urethral os, vaginal canal, and cervix. Hysteroscopy allowed visualization of the uterine endometrium and facilitated endometrial biopsy collection. Additionally, ultrasonography was utilized to identify ovaries in several bears, offering insights into ovarian dynamics and follicular development. Several abnormalities were noted during examinations of both in vivo and ex vivo tracts; these included clitoral hypertrophy, vaginal strictures, uterine polyps, endometritis, and cystic hyperplasia, although it is unclear if these aberrations significantly impacted fertility. Findings contribute to a better understanding of polar bear reproductive anatomy, highlight the utility of diagnostic techniques for monitoring reproduction, and elucidate potential causes of reproductive failure in polar bears.