Humans have a right to bodily autonomy, that is they have the right to decide how and for what their body is used. As such, a woman has a right to decide whether or not her body is used to support a fetus, and her right supersedes any right to life that the fetus may have. The only thing we truly own is our own body. It is the only thing that remains with us from the moment of our birth to the moment of our death. As such, we ought to have the right to decide how and for what our bodies are used. Because of that right, we are not morally required to provide the use of our bodies to others. Therefore, a woman is not morally required to provide the use of her body to a fetus.  Another human right accepted by most people is a right to life. However, a right to life has limitations. It means people have a right not to be killed unjustly. It does not mean someone has a right to anything that will sustain their life. That means that an ill patient does not have the right to the use of another person's body just because they are ill. For instance, while donating a kidney might be morally good, failure to do so is not morally bad. Few would claim that if someone were to die because you failed to donate a kidney, it would be your fault. This can be compared to pregnancy. While it might be good of you to carry a pregnancy to term, it is not required of you to provide your body for the use of the fetus.
While a woman has the right to choose what to do with her body in most cases, it is not clear that she has the right to use her body in ways that harm other people. There is a difference in cases where we donate organs. Lots of people can donate organs and save lives. An infant, however, is only able to survive within one person. Because of that, a mother has a greater level of responsibility towards the infant. Furthermore, whenever a woman has sex voluntarily, she is accepting the chance of her becoming pregnant. As that is the case, she is, in a sense, volunteering her body to be used by a fetus. To continue with the organ analogy, most people would consider it wrong to suddenly decide you will not donate an organ after promising an individual to give them what they need.
[P1] Human beings have a right to bodily autonomy. [P2] A human being has no moral obligation to let their body be used by another human being. [P3] A fetus uses a woman's body. [P4] A woman is not obliged to sustain the life of the fetus.