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A type of abortion banned under a new federal law would cause "severe and excruciating" pain to 20-week-old fetuses, a medical expert testified Tuesday in one of three trials across the country testing the law's constitutionality.

"I believe the fetus is conscious," said Dr. Kanwaljeet "Sonny" Anand (search), a pediatrician at the University of Arkansas for Medical Sciences. He took the stand as a witness for the government, which is defending the Partial-Birth Abortion Ban Act (search).

Anand later acknowledged that he believes a less controversial abortion procedure, known as "dilation and evacuation," would cause the same amount of pain to a fetus. An estimated 140,000 D&Es, the most common method of second-trimester abortion, take place in the United States annually.

He also said there is no medical definition of "consciousness."

The law, signed by President Bush in November, has not been enforced because judges in Lincoln, Neb., New York and San Francisco agreed to hear evidence in three simultaneous, non-jury trials on whether the ban violates the Constitution.

Anand said Tuesday that fetuses show increased heart rate, blood flow and hormone levels in response to pain.

"The physiological responses have been very clearly studied," he said. "The fetus cannot talk ... so this is the best evidence we can get."

The Bush administration has argued that the procedure, referred to by opponents as "partial-birth abortion," is "inhumane and gruesome" and causes the fetus to suffer.

During the procedure, which doctors call "intact dilation and extraction" or D&X, a fetus is partly removed from the womb and its skull is punctured. It is generally performed in the second trimester.

Abortion rights advocates argue that it is sometimes the safest procedure for women, and that the law will endanger almost all second-trimester abortions, or 10 percent of the nation's 1.3 million annual abortions.

Another government witness, Dr. Leroy Sprange, who practices obstetrics and gynecology in Illinois, said he has never performed a D&X but he believes it increases the risk of infection and causes undue trauma to the cervix.

"I've never seen a situation where intact D&X is the safest or best procedure to preserve the health of the mother," Sprange said Tuesday.

The law would be the first substantial limitation on abortion since the Supreme Court legalized it 31 years ago in the landmark Roe v. Wade (search) case.

Challenges to the ban were filed by several doctors being represented by the Center for Reproductive Rights (search), the National Abortion Federation (search) and the Planned Parenthood Federation of America (search). The issue is expected to reach the Supreme Court.