His most famous abortion opinion, a 1991 dissent in Planned Parenthood v. Casey, would have upheld a Pennsylvania law that required women seeking abortions to notify their husbands. "Pennsylvania has a legitimate interest in furthering the husband's interest in the fate of the fetus," Judge Alito wrote. The United States Supreme Court rejected his position the next year.
In a series of less noticed cases concerning asylum requests based on claims of forced abortions abroad, Judge Alito ruled that marital status could be the determining factor.
Last year, he ruled that the husbands of women forced to undergo abortions in China had themselves suffered persecution serious enough to warrant granting the men asylum in the United States. But he rejected similar claims from boyfriends or fiancés of women who had been forced to have abortions.
The categorical distinction was warranted, he wrote, because marriage was a central organizing principle in the law. "The marriage relation," he wrote, is important in "so many areas," including "income tax, welfare benefits, property, inheritance, testimonial privilege, etc."
Extending the asylum protection "to nonspouses would create numerous practical difficulties," he wrote.
After abortion, the legal definition of marriage may be the most divisive issue in American law, and Judge Alito will almost certainly hear cases concerning the rights of gay and lesbian couples if he is elevated to the Supreme Court.
While he has clearly given the legal status of marriage a great deal of thought and has seemed to endorse a traditional understanding of it, he has not participated in any significant cases involving gay rights. People on both sides of the gay marriage debate will be reading many of Judge Alito's abortion opinions with intense interest.
The word "abortion" appears in 22 decisions in which Judge Alito participated in his 15 years on the United States Court of Appeals for the Third Circuit, in Philadelphia, according to searches of legal databases. But seven of those references are passing ones. In the remaining 15 cases, questions about abortion played an important role.
The decisions are not easy to categorize. Judge Alito voted in support of the abortion rights side of the argument in three cases, apart from Casey, that most directly presented questions about the legal status of abortion and of restrictions on it.
In 1997, he joined a decision applying the Supreme Court's 1973 decision in Roe v. Wade, which established a constitutional right to abortion, to uphold a New Jersey law that let parents sue on behalf of deceased children but not stillborn fetuses.
In 2000, he joined a decision applying Stenberg v. Carhart - another 2000 decision that struck down a Nebraska law that banned a procedure its critics call partial-birth abortion - to a similar New Jersey law.
In both cases, though, Judge Alito wrote separate concurrences, carefully calibrating his language and reasoning to set out no more than he wanted to say. In the 1997 decision, for instance, he wrote to fine-tune and limit some of the language in the majority's decision.
"I think that the court's suggestion that there could be 'human beings' who are not 'constitutional persons' is unfortunate," Judge Alito wrote. "I agree with the essential point that the court is making: that the Supreme Court has held that a fetus is not a 'person' within the meaning of the 14th Amendment. However, the reference to constitutional nonpersons, taken out of context, is capable of misuse."
In 1995, he cast the deciding vote in a 2-to-1 decision striking down parts of a Pennsylvania law that restricted abortion. The law, the Pennsylvania Abortion Control Act, included a provision that required a doctor's certification in cases in which a publicly funded abortion was being performed because the woman's life was said to be in danger.
The certification had to be signed by a doctor other than the one about to perform the abortion and without a financial interest in it. Judge Alito joined the majority decision written by Judge Robert E. Cowen striking down the certification requirement and a second restriction because they conflicted with federal Medicaid regulations.
A dissenting judge, Richard L. Nygaard, said the majority's approach represented "deference run amok."
It is nonetheless Judge Alito's 1991 dissent in Casey that has attracted the most interest, partly because the case went on to become the vehicle for the Supreme Court's reaffirmation of Roe v. Wade in 1992.
Eight of Judge Alito's abortion decisions arose in immigration cases involving Chinese nationals seeking asylum in the United States.
People who can show that they are unwilling to return to their country because they fear persecution based on their race, religion, nationality, membership in a social group or political opinions are eligible for asylum under a federal law. The law says that someone "who has been forced to abort a pregnancy or to undergo involuntary sterilization" also qualifies.
The Board of Immigration Appeals ruled in 1997 that husbands were eligible for asylum based on their wives' forced abortions. Last year, Judge Alito, writing for a unanimous three-judge panel, declined to extend that decision to boyfriends and fiancés.
The petitioner in the case, Cai Luan Chen, argued that he would have married his fiancée but for, as Judge Alito's decision put it, "China's inflated minimum marriage age requirement, which was instituted as part of the country's oppressive population control program." (The minimum age for men to marry in China is 22.)
Judge Alito expressed some sympathy for the argument but concluded that marriage was a categorical status that was easily applied to particular cases and was central to many distinctions made in the law.
The United States Court of Appeals for the Ninth Circuit in San Francisco reached a contrary conclusion in an asylum case last year, saying "husbands whose marriages would be legally recognized but for China's coercive family planning policies" could be entitled to asylum.
When two federal appeals courts issue flatly differing decisions on a decisive legal question, the Supreme Court often agrees to hear a case presenting the question to resolve the difference.
Judge Alito has rejected asylum applications involving abortion in other cases as well.
Last month, for instance, he joined an unsigned opinion for a three-judge panel that rejected a Chinese woman's request. She said she had been forced to have an abortion in China and feared she would be sterilized if she returned.
An immigration judge concluded that the woman was not credible. The appeals court panel agreed, reciting some of the contradictory evidence that she had offered about the abortion and her marriage to a man called "her purported husband" by the panel.
In a 2003 decision, Judge Alito affirmed a lower court's decision that a Chinese woman's claim that she had been forcibly sterilized was not credible. The lower court relied in part on "the lack of a statement from her husband about her opposition to her own sterilization," a factor Judge Alito indicated was entitled to some weight.
He went on, however, to say the lower court's decision had not turned on the husband's failure to participate in the case.
In two other cases in which he considered the evidence stronger, Judge Alito, both times writing for a unanimous court, returned asylum cases to a lower court for further fact-finding, with the strong suggestion that the courts had erred in rejecting the asylum cases before them.
Abortion also played a role in an employment discrimination case brought by a nurse against the New Jersey hospital where she worked. The nurse, Yvonne Shelton, refused to participate in procedures that she considered abortions. The hospital offered her another job, in an intensive care unit for newborns. She declined it, and the hospital fired her.
The panel agreed that Ms. Shelton's decision not to participate in abortions warranted protection on religious grounds. But Judge Anthony J. Scirica, writing for a unanimous three-judge panel that included Judge Alito, found that the hospital had acted appropriately.