From 1973 to 1989, Roe vs. Wade was the law of the land. That landmark case stated that there is a constitutional right to privacy which "encompasses a woman's decision whether or not to terminate her pregnancy."
That right was, in effect, unrestricted in the first trimester of pregnancy. But the court said the state had the right to regulate abortion to protect maternal health from the beginning of the second trimester of pregnancy until the fetus becomes viable, at about the beginning of the third trimester. And it said that after viability a state may prohibit abortions, except those necessary to preserve the life and health of the mother.
Though often attacked legally and politically, and though slightly modified by successive Supreme Court decisions, it was not until 1989 that the high court truly undercut Roe. Then a five-justice majority upheld Missouri abortion laws in conflict with Roe in a way that invited other states to go beyond Roe. Four justices said in that case -- Webster vs. Reproductive Health Services -- that Roe should be reversed.