HELLP syndrome

HELLP syndrome is a problem that shows up during pregnancy or in the postpartum period, the stretch of time right after giving birth. Its name is an acronym that pulls together what happens in the blood and the liver: hemolysis, which means red blood cells break apart; elevated liver enzymes, substances from the liver that come back high on blood tests; and low platelets, meaning too few of the tiny cell fragments that help blood form clots.

Inside the body, the story starts in the placenta. Its blood supply depends on vessels called spiral arteries, and in HELLP syndrome these arteries fail to remodel, meaning they don't go through the change in shape they're supposed to make. The placenta becomes ischemic: it gets less blood than it needs. That activates the endothelium, the thin layer that lines the inside of blood vessels. Platelets stick to that activated lining and get used up, which is why their numbers drop.

Capillaries, the body's tiniest blood vessels, end up loaded with platelets and fibrin, a protein that forms the strands in a blood clot. Picture a narrow hallway with threads strung from wall to wall: red blood cells have to make their way through it, and they get torn apart along the way. That's hemolysis. In the liver, necrosis also develops, meaning patches of tissue die. About 70% of cases appear in the third trimester of pregnancy, and the rest within 48 hours after delivery.