Delayed miscarriage inside an infected decidual cast: a rare complication of the Depo medroxyprogesterone acetate injection.

Decidualisation of the endometrium is a progesterone-mediated reaction that naturally occurs during a woman's menstrual cycle. The hyperproliferated tissue is then usually dissolved and passed in a menstrual period. Occasionally, the natural dissolution does not happen, and the tissue maintains the shape of the endometrium, forming a decidual cast. These casts are known to be formed secondary to the use and/or cessation of various contraceptive methods. Here, we report a case of a patient presenting with passage of a decidual cast secondary to cessation of the Depo medroxyprogesterone acetate injection. This is the first reported case of the cast becoming infected, and also the first case of a decidual cast containing old products of conception.