By signing into law a bill which bans a form of late abortion known as 'partial birth' terminations, US President George Bush has authorised the most significant federal restriction on abortion since it was made legal 30 years ago. A number of critics have already mounted legal challenges. BBC News Online looks at the issues surrounding the ban on partial-birth abortions.
What is a partial birth abortion and at what stage is it carried out?
The term itself is not a medical one. It is believed to refer to a procedure known as dilation and extraction. Pro-choice lobbyists say the term "partial-birth abortion" has been coined by those opposed to it because it is more emotive.
Partial-birth abortion is one in which the foetus is partially delivered before the pregnancy is terminated. This usually involves extracting the foetus, feet first, from the womb, and through the birth canal until all but the head is exposed.
Surgical scissors are inserted into the base of the skull, a suction catheter is inserted through the opening and the brain is removed.
The procedure would not normally be used until 20 weeks into a pregnancy. Most are performed late in the second trimester, which ends at 27 weeks into pregnancy. However, "partial-birth" abortions can be carried out right through to the ninth month of pregnancy.
Why are they carried out?
Some members of the pro-choice lobby and a number of doctors argue that partial-birth abortion is a necessary procedure, usually carried out when the life or health of the mother is at risk, or the foetus is severely disabled.
However, opponents say that in many cases the procedure is carried out when it is not medically necessary to save the life of the mother.
They also argue that it sometimes used for what they define as social reasons - for instance, when the mother is suffering from depression.
Why do some people want a blanket ban?
Many opponents of abortion believe that a partial-birth abortion is a particularly traumatic procedure. They argue that a foetus is "viable" towards the end of the second trimester - that it could potentially live if born at this stage.
They also argue that during the second trimester the foetus has become sensitive to pain.
Why are legal challenges being mounted?
Critics have mounted challenges in courts in New York City, San Francisco and Nebraska questioning the constitutionality of the law. They want it temporarily blocked and ultimately overturned.
Their main argument is that the law does not have an exception to protect a woman's health. It does, however, have one to protect a woman's life.
Hours after Mr Bush signed the bill into law, a federal judge in Nebraska blocked it from applying to four doctors who had brought a case against it.
Judge Richard Kopf took issue with the lack of an exception in the law to protect a woman's health. He described it as "highly suspect, if not a per se violation of the constitution."
His ruling means that the law can not be enforced against the four doctors - who practice in or are affiliated with practices in more than a dozen states. It also protects anyone the doctors work with or to whom they refer patients.
Former President Bill Clinton vetoed two similar bills on the grounds that they lacked an exception to protect the health of the mother. And, in 2000, the US Supreme Court invalidated a similar Nebraska law barring the procedure for the same reason.
However those involved in putting together the partial-birth abortion ban say they have taken that court's objections at that time into account.
President Bush has vowed to fight the lawsuits.
What are the likely political implications?
All nine Democrat candidates for the presidency oppose restrictions on abortion rights and a number have criticised President George Bush for signing the law.
Contender Joe Lieberman said the law "utterly disregards the safety and well-being of the mother", while a second, doctor-turned-politician Howard Dean, declared it a "dark day for American women".
However, it remains unclear to what extent they would focus on this during an election campaign. A recent USA Today/CNN/Gallup poll found that seven in 10 Americans support the ban on partial-birth abortion and some 65% of House and Senate members voted last month in favour of the bill.
Many of those who describe themselves as pro-choice say they feel uneasy about the partial-birth procedure. As such, analysts note, the political mileage in adopting the partial-birth abortion cause would be limited.
Will there be further encroachments on a woman's access to abortion?
Opponents of the ban on partial-birth abortions stress that the bill will not just outlaw a necessary form of abortion - its wording is vague enough to outlaw other forms of terminations.
But, while many Americans oppose the partial-birth procedure, support for the principle of Roe v Wade, the court ruling which made abortions legal, remains high.
President Bush recently acknowledged that popular opinion had not changed "to the extent that the American people or the Congress would totally ban abortions."
With an election looming, Mr Bush also has to ensure he retains the support of moderate suburban women, many of whom support abortion rights.
Nonetheless, anti-abortion activists see the ban on this procedure as a significant step in the right direction, and as such are encouraged by it. They are hoping for further gradual restrictions on women's access to abortion.