A 32-year-old woman who is 36 hours postpartum experiences lower abdominal pain, fever, flu-like symptoms, a tender uterus that is subinvoluted, and foul-smelling discharge. Which of the following is most consistent with this presentation?

Choice A reason: Trichomonas is a sexually transmitted infection that typically causes vaginal discharge, itching, and irritation. It does not cause uterine tenderness or systemic symptoms like fever and flu-like illness in the postpartum period. Choice B reason: A urinary tract infection may cause fever and abdominal discomfort, but it does not typically result in a tender, subinvoluted uterus or foul-smelling lochia. The symptoms described are more consistent with a uterine infection. Choice C reason: Endometriosis is a chronic condition involving ectopic endometrial tissue, causing pelvic pain and infertility. It is not an acute postpartum infection and does not present with fever or foul-smelling discharge. Choice D reason: Endometritis is an infection of the uterine lining, commonly occurring postpartum, especially after prolonged labor or cesarean delivery. Symptoms include uterine tenderness, fever, subinvolution, and malodorous lochia. This diagnosis best fits the clinical presentation.