Bitches have the slowest uterine involution of all domestic species. It can take up to 90 days to complete. Normal repair of the endometrium at the placental attachment sites can take as long as 12 weeks. The postpartum discharge of fetal fluids and placental remains (lochia) is normally present for 3–4 weeks after parturition. Initially, the lochia is greenish and then becomes more red-brown. The amount of lochia should slowly decrease. Subinvolution of the placental sites (SIPS) should be suspected if serosanguineous vaginal discharge persists for > 6 weeks.
Pathogenesis of Subinvolution of Placental Sites in Small Animals
The pathogenesis of SIPS is unclear. During formation of the placenta, the cells from the developing embryo invade into the endometrium. After the placentas detach following whelping, the placental sites normally heal by sloughing these invading cells. In some cases, however, these cells continue to persist in the uterine wall, resulting in continued hemorrhage from the placental sites.
SIPS generally occurs in young bitches and usually after the first litter.
Clinical Signs of Subinvolution of Placental Sites in Small Animals
Subinvolution of the placental sites is clinically characterized by serosanguineous (yellowish-red) to hemorrhagic vaginal discharge beyond 6–8 weeks after parturition.
Diagnosis of Subinvolution of Placental Sites in Small Animals
Diagnosis of subinvolution of the placental sites is based on clinical signs and history and signalment.
Vaginal cytologic findings include syncytial trophoblast cells 4 weeks after parturition.
Other diagnostic tests include diagnostic imaging and biopsy of placental sites (rare).
Usually, it is a diagnosis of exclusion.
Treatment of Subinvolution of Placental Sites in Small Animals
Oral administration of low doses of progestogen (eg, megestrol acetate) for 2 weeks has been reported to be effective in stopping persistent serosanguineous vulvar discharge in bitches with subinvolution of the placental sites. The amount or composition of the discharge does not change with antimicrobial treatment but can be considered to prevent infection due to the presence of persistent uterine fluid. However, most of the affected animals are systemically healthy. Cautious monitoring of blood loss is generally the recommended treatment.
Should vaginal bleeding not subside, further investigation is warranted to rule out clotting disorders, trauma, and neoplasia. In severe cases, a blood transfusion may be necessary (rare).
Ovariohysterectomy is indicated in rare cases of profound permanent bleeding or uterine infection. Uterine contracting agents (oxytocin and ergonovine) are not recommended and are not effective.
Cases of SIPS generally spontaneously resolve when there are no other clinical signs aside from prolonged vaginal discharge. The prognosis is excellent, and future fertility is not affected by this disease.