All of the reasoning boils down to two essential question. do women have the right to determine their own medical care? Do we consider having an abortion to be a medical procedure? If the answer is yes to both, then the laws concerning privacy and individual autonomy are paramount.
Preeclampsia is diagnosed in 2-8% of women worldwide and is responsible for about 15% of premature birth in the United States alone. 2-10% of pregnant women develop gestational diabetes. 1,600 women die every day worldwide from childbirth. Infections both associated with birth and the administration of the epidural is risk. there is risk at every stage of the pregnancy, including birth, which could result in lifelong complications and possible death. This is not a question of a speculative bad outcome, it is a statistically measured risk of any number of complications. For me to be exhaustive of that list, I would need to write a multi-page response. Men do not face these risks, it is entirely on women.
Your analysis of social contracts puts too much weight on a philosophical idea, which a social contract is. Social contracts are not enforceable as a matter of law. They are moral and ethical theories that were popularized by figures such as Hobbes and Locke.
Common law is made up of judicial precedent, which may have reasoning rooted in custom and tradition, but is ultimately predicated on judges looking back to past judicial decisions and updates in the statutory code. It is based on English common law. Statutory law supersedes common law (though the supreme court determines whether statutory law is constitutional).