How often do women die from giving birth to multiples?

Very rare. There are certainly many risk of multiple pregnancy to a mother such a high blood pressure, diabetes of pregnancy and cesarean section. And yes technically there is a higher rate of death of the mother. But that risk is extremely small (something on the order of 1/10, 000).
More than singletons. Multiple pregnancy is a poor outcome of fertility therapy, for both moms and babies. Maternal mortality, while rare, is 5-10 times more common with twins compared to singleton pregnancy.