There are a host of reasons why a woman can die during childbirth. In developed nations, where childbirth is tended to medically, the problems are most often caught and treated before death occurs, but in underdeveloped nations, medical intervention is not the norm and is either difficult or impossible to obtain. That's why mortality rates are so much higher there. Here are some of the things that can go wrong:
Blood pressure can go through the roof and mother dies of a stroke.
Baby gets stuck, or cervix doesn't dilate properly and mother dies of exhaustion, since labor will continue until either baby is born or mother is dead.
The placenta can sometimes detach from the wall of the uterus (called placental abruption) before baby is delivered. Hormones to shut down blood supply and contract the uterus don't happen until after baby is born, so in the instance of an abruption, the mother continues to hemmorage. That amount of blood loss can cause death within minutes.
There are also problems that can arise immediately following birth which can cause death, and they also fall into the category of blood pressure problems and bleeding.
Some of the causes of death of women while giving birth include; severe bleeding or hemorrhage, infections, obstructed labor, unsafe abortions, deep vein thrombosis, anemia, malaria, cardiovascular disease or stroke from high blood pressure, among other causes.
what I didn't notice in any of the other answers you received is Giving childbirth is extremely stressful to the body of the soon to be Mother. The heart is pushed to the extremes the blood vessels and arteries are pushed almost and in some cases past their limits. The lungs are overworked as are the kidneys these all play a part in the miracle of child birth. God bless the Mothers