Toxemia of pregnancy (pre-eclampsia) threatens the life of a mother. I should know, I had two, but I received excellent care and had two healthy children, and of course, didn't die. ;-D
Lot's of things can "threaten" the life of the mother, heck pregnancy itself is hardly risk free. But the only condition I am aware of where abortion is the only (or even a good) option is tubal (ectopic) pregnancy. And in that case the baby can't survive anyway.