Her life is more valuable than the baby because she has actually lived, has friends and family, possible a job or hobby, and is a contributor to society. It may sound harsh but that's life. But I do think you should save both.
Not to mention that, from a less humanistic approach and a more mechanical approach, a living woman capable of bearing more children (unless said children would threaten her life) is more beneficial to the survival of the species than a single child whose life caused the death of their mother and then has to wait 15 years to reach sexual maturity.
It's funny because essentially the right-wing's "Blargh, women are only for babies, and the baby's life is more important than the mother's!" attitude is actually causing LESS births.
...Of course, I support birth control and pro-choice stuff entirely. And do not desire the slightest bit to make a woman into a baby mill. That's just horrible.
Not to mention that our species is quite capable of breeding itself out of survival rather than keeping survival.