A case of uterine hematoma in a mare after an endometrial biopsy

Endometrial biopsy is an important, safe and painless procedure to assess equine uterine health. While minor bleeding at the site of sampling is a common condition, uterine hematoma is a rare complication. An endometrial biopsy was routinely performed on an unsedated 17 year-old welsh pony mare in estrus during a research protocol. From the next day on and during the following 7 days, a large amount of sanguineous fluid was observed in the uterine cavity during the daily ultrasound examination performed according with the protocol. No fever or any other systemic symptoms were noticed. Two weeks later, the ultrasound examination revealed an organised hyperechogenic mass compatible with a hematoma within the endometrial lumen. The mare was regularly controlled during the rest of the breeding season and no abnormalities in her cyclicity were observed. The size of the hematoma only began to decrease from the 3rd month after the biopsy onward and it disappeared completely 2 months later. This was the only complication following a biopsy in this study protocol that included a total of 70 biopsies on 49 mares and the very first case the authors got to see while biopsies have been common practice in their clinical and research activities for years. To our knowledge, this is the first time that the appearance of this condition is documented. The hematoma took 5 months to disappear at the ultrasound examination. During this time the mare could not be bred. Therefore, while endometrial biopsy should still be regarded as a safe procedure for the diagnosis of infertility in mares, the potential risk of a hematoma with its consequences for the breeding season has to be considered.