Mid-gestational luteal insufficiency in predisposed dog breeds: Retrospective evaluation of medroxyprogesterone acetate therapy and timed-withdrawal.

Background and Aim: Hypoluteodism is an important cause of non-infectious pregnancy loss in bitches and is characterized by inadequate progesterone (P4) production by the corpus luteum. Evidence regarding breed-specific patterns of luteal insufficiency and the clinical utility of medroxyprogesterone acetate (MPA) with timed-withdrawal remains limited. This study aimed to identify the temporal pattern of luteal insufficiency in predisposed dog breeds and to evaluate the efficacy and safety of an MPA protocol combined with standardized late-gestation withdrawal. Materials and Methods: Clinical records from 29 pregnancies in 25 bitches diagnosed with hypoluteodism were retrospectively reviewed. The cohort consisted predominantly of Shetland Sheepdogs (21), together with Miniature American Shepherds (2) and Pomeranians (2). Serial serum P4 monitoring commenced during the fourth week of gestation. Hypoluteodism was diagnosed when P4 concentrations decreased below 10 ng/mL or declined by >5 ng/mL within 48-72 h. A low-dose MPA regimen (0.1 mg/kg, orally, once daily) was administered, and treatment was discontinued 24-48 h before elective cesarean section. Pregnancy outcomes and maternal and neonatal safety parameters were evaluated. Results: A distinct mid-gestational critical window was identified, with 79.3% of cases exhibiting P4 decline during weeks 5-6 of gestation. Pregnancy was successfully maintained to term in 86.2% (25/29) of pregnancies. Reproductive failure occurred in four pregnancies (13.8%), including three abortions and one case of fetal mummification. Mean litter size was approximately 4.4 puppies, yielding 110 live-born neonates, of which 94.5% survived to weaning. Female puppies showed no evidence of virilization, and no maternal complications, including diabetes mellitus, mammary hyperplasia, mammary tumors, or agalactia, were observed. Timed-withdrawal of MPA before delivery prevented premature labor and fetal compromise. Conclusion: Predisposed breeds, particularly Shetland Sheepdogs, exhibit a predictable period of luteal vulnerability during weeks 5-6 of gestation. Early P4 surveillance beginning at day 28-30 post-ovulation, combined with low-dose MPA therapy and withdrawal 24-48 h before elective delivery, represents an effective clinical strategy for reducing pregnancy loss while facilitating planned cesarean section.