Women who use abortion pills rather than the more common surgical method seem to face no greater risk of tubal pregnancy or miscarriage in later pregnancies, according to a new study.

The federally funded research — based on nearly 12,000 Danish women — is considered the best study to date of the impact of this newer abortion method on subsequent pregnancies.

The vast majority of abortions are called surgical abortions, usually done by vacuuming an embryo or fetus out with a syringe or electric pump.

The U.S. and Danish researchers studied medical abortions. Generally, it involves a woman ending a pregnancy by taking one tablet of mifespristone — formerly known as RU-486 — followed by about four misoprostol pills a day or two later. The mifepristone destabilize the connecting tissue between an embryo and the uterus, and the misoprostol causes the uterus to expel the embryo.

Medical abortions appeal to women because they can do it in the privacy of their home, can seem less intimidating than surgical abortion and just about any doctor can prescribe the pills, experts said.

The U.S. government approved the marketing of mifepristone for medical abortions in 2000, and European countries approved it years earlier.

Today, an estimated 8 to 10 percent of the roughly 1.3 million abortions in the United States are done using the pills.

While previous research has shown surgical abortions don't increase the risk of problems in later pregnancies, little research had been done into the impact of medical abortions.

Generally, surgical abortions completely remove an embryo or fetus and surrounding uterine tissue but abortions done with pills may leave bits of placenta or other embryonic material. Some doctors have wondered whether that might interfere with subsequent pregnancies, said Dr. Matthew Reeves, a reproductive medicine expert at the University of Pittsburgh School of Medicine.

"This kind of squashes any concerns," said Reeves, who was not involved in the study.

The paper is published in Thursday's New England Journal of Medicine.

In the new study, researchers used a national abortion registry to identify all women in Denmark who had abortions between 1999 and 2004, and then got information on later pregnancies from national patient and birth registries.

Denmark is the only country with an abortion registry, said study co-author Dr. Jun "Jim" Zhang of the National Institutes of Health.

They looked at tubal pregnancies, in which a fertilized egg implants outside the uterus — usually in the fallopian tubes. Such a situation fails to nurture the embryo and endangers the mother.

The new study found tubal pregnancies occurred at the same frequency — about 2.5 percent of the time — in both the medical and surgical groups. The rates of miscarriage, early deliveries and low birth weight babies also were similar.

Researchers were unable to take into account mother's history of smoking, previous tubal pregnancies or other factors not detailed in the registries. But they believed it did not affect their results.

Generally, the number of reported abortions in the U.S. have been declining since the early 1990s, although there was a slight increase in 2002, according to federal statistics. There is about one abortion for every four live births each year, according to the CDC's most recent statistics, which do not include every state.