Final answer:
Most advanced nations of the world limit elective abortions after 24 weeks of gestation. In the United States, abortion is allowed prior to the viability of the fetus, which is usually around 25 to 28 weeks.
Step-by-step explanation:
Most advanced nations of the world limit elective abortions after 24 weeks of gestation.
In the United States, the right to an abortion prior to the viability of the fetus was deemed protected by the Constitution in the historic Supreme Court decision Roe v. Wade (1973). The court established a trimester system to guide abortion decisions.
The court initially acknowledged an unmitigated right to abort in the first three months of pregnancy but left it up to the government to regulate abortion in the second trimester and restrict or ban it in the last trimester if the life of the person carrying the pregnancy was not in danger.
A subsequent Supreme Court decision, Planned Parenthood v. Casey (1992), reaffirmed Roe v. Wade and ruled that state abortion regulations could not place serious obstacles in the path of someone who chose to seek an abortion before a fetus was viable. The decision also replaced the trimester system with the notion of fetal viability or the fetus's ability to survive outside the womb (approximately at 25 to 28 weeks). Someone therefore cannot freely seek an abortion if the fetus is viable.