"But I must persist that once you recognize a right to life, the most fundamental right, the imposition on the mother (whose actions, lest we forget, are cause of the existence of the fetus in the first place) cannot outweigh the interest of the fetus in continuing to survive"

The woman's rights are not trumped. We are protected against indentured servitude by the Constitution. This certainly would be the case if you force a woman to be pregnant against her wishes for nine months which could result in her death. Yes, women still die in childbirth. You cannot force me to use my body to host anything, you cannot force me to provide a lung for transplant, for example.

A clump of cells, wether they will grow into a baby or not, doesn't trump the rights of the woman.

Why is this "(whose actions, lest we forget, are cause of the existence of the fetus in the first place)" so central to your argument? Could this be about punishing the woman for having sex? And what of the father? They make contraception for men, too. It takes two to tango. Hmmm.. I'm not so sure you are simply worried about the fetus.