Chorioamnionitis

Chorioamnionitis — also called intraamniotic infection or 'triple I' — is an infection of the fetal membranes and amniotic fluid, most often caused by polymicrobial ascent of vaginal flora (GBS, E. coli, anaerobes). It's a classic obstetric emergency that USMLE Step 1 tests in two narrow ways: recognizing the clinical diagnostic criteria and knowing the management, specifically that delivery cannot wait. The concept appears in vignettes involving prolonged rupture of membranes, prolonged labor, or multiple vaginal exams — all classic risk factors that set the scene before dropping the diagnosis on you.

The trickiest part is the diagnosis itself. Students either try to pin it on a single lab value (leukocytosis alone, or a positive culture) or they miss that fever is the anchor criterion — you need fever plus at least one additional finding. USMLE Step 1 will give you a febrile laboring patient and ask what else you need to confirm the diagnosis, or present all the criteria and ask you to name it. No single lab test confirms chorioamnionitis; it's a clinical call.

Management is where the classic wrong answer lives. Students trained to 'treat the infection first, then reassess' will defer delivery — and that's the trap. The infected placenta cannot be sterilized in utero. Antibiotics alone are not sufficient. Step 1 expects you to know that prompt delivery, regardless of gestational age, plus broad-spectrum antibiotics (typically ampicillin + gentamicin) is the correct answer. Deferring delivery costs points every time.