Risk of bleeding! Sometimes abnormal placentas begin to breakdown at 20wks, leading to exposure of mom to some of dad's placental genes and lead to an "allergic" reaction where the vessels spasm and platelets are drawn away (thrombocytopenia). The spasm causes high BP, HA, liver dysfunction, vision changes, and protein in the urine; leads to maternal seizure, decreased baby growth, and sometimes placental abruption.
Bad. Severe preeclampsia is a marked increase in blood pressure along with swelling and protein in your urine. It can have serious consequences for you and/or the baby. Hellp syndrome is a variation of severe pre eclampsia that has hemolysis, elevated liver tests and low platelets that can be very dangerous. Most women with hellp or severe preeclampsia are delivered shortly.