Some experts predict the percentage of such "medical abortions," which offer more privacy than surgical termination at an abortion clinic or hospital, will rise even more due to the new study.
The research, done at Planned Parenthood clinics across the country, shows that a new way of giving pills to induce abortion virtually eliminated the risk for a rare but dangerous infection.
"This is the first really huge documentation of how safe and effective medical abortion is," said Dr. Beverly Winikoff, a professor of family health and population at Columbia University. "The technology is very good and very well used in this country, and probably will be used more and more."
Two pills are used to induce an abortion. The primary drug, Mifeprex, was first approved in the U.S. in 2000. Use has risen steadily, even though manufacturer Danco Laboratories LLC of New York hasn't promoted it and the drug can only be obtained at a clinic or doctor's office, not through a pharmacy. Sales rose 16.5 percent last year, when about 184,000 American women used Mifeprex.
Medical abortions now account for about a quarter of early abortions, according to company spokeswoman Abby Long. At Planned Parenthood, the biggest provider of medical abortions, they amount to 32 percent of early terminations.
The group's study analyzed medical abortions at Planned Parenthood centers between 2005 and mid-2008 - about 228,000 cases. It found the abortion pill was about 98.5 percent effective and that changes in how the drugs were given reduced risk of a serious infection from barely 1 in 1,000 cases to 0.06 in 1,000.
The results are reported in Thursday's New England Journal of Medicine.
The procedure, which works during the first nine weeks of pregnancy, involves swallowing Mifeprex, known chemically as mifepristone, at a doctor's office. Originally known as RU-486, the pill causes an embryo to detach from the uterine wall. A second pill, misoprostol, is used 24 to 48 hours later to cause contractions and push the embryo out of the uterus.
These drugs are different from Plan B, which is taken within a couple days of contraceptive failure or unprotected sex to prevent pregnancy from occurring.
Originally, the procedure involved inserting the misoprostol pill into the vagina where the medicine was absorbed. But by the end of 2005, four American women and one Canadian had died of a rare bacterial infection afterward, spurring concern among providers and criticism by abortion opponents.
So in April 2006, Planned Parenthood told its 300 clinics offering the procedure to instead have patients put the misoprostol pill in their mouth and let it dissolve.
Some clinics also began providing a week's course of antibiotics to avoid infection; the others tested women and treated any with sexually transmitted diseases. In 2008, all the clinics started giving patients antibiotics.
"We decided we needed to make a safe procedure even safer," said the study's lead researcher, nurse practitioner Mary Fjerstad.
By the study's last six months, serious infections had declined to one-16th of the original rate.
"I think that providers are going to be pretty impressed with the data," said Dr. Beth Jordan, medical director of the Association of Reproductive Health Professionals, which plans to highlight the findings to doctors, nurse practitioners and pharmacists at its annual meeting in September.
Given that 87 percent of U.S. counties have no abortion provider, Jordan said the findings might encourage some primary care doctors to offer abortion using the pills.
"But I don't think it's going to open the floodgates," she said.
In October, the National Abortion Federation, representing 400 centers that provide more than half of abortions in the U.S. and Canada, will review the findings and decide whether to make changes accordingly. Federation President Vicki Saporta said current guidelines allow putting misoprostol in the cheek to dissolve, swallowing it, or inserting it in the vagina, which more than a third of her member clinics do.
Saporta said abortion opponents "have been misleading people into thinking that medical abortion is unsafe," but the study proves the procedure is safe. The cost is $400, only slightly less than the median cost for an early term surgical abortion.
Since approval in 2000, there have been six deaths from sepsis, a bloodstream infection, among the more than 1.1 million American women who have used Mifeprex, most recently one in July 2007. That's a death rate of less than 1 in 167,000, according to the maker, and less than 0.1 percent of patients have needed transfusions.
Misoprostol, which is officially approved in the U.S. for preventing stomach ulcers, is sold under the brand name Cytotec and made by Pfizer Inc.
Winikoff and Saporta both raised concerns about giving a full course of antibiotic treatment to all women to prevent very few infections - unlike the brief preventive dose given with surgical abortions. They said that could trigger a rare allergic reaction, add to the problem of antibiotic resistance and add to the cost of the procedure - making it unaffordable in developing countries.
Chris Gacek, a senior fellow at the anti-abortion Family Research Council, said he wasn't surprised by the increasing use of Mifeprex.
"I don't think at this point we're going to do anything" to try to limit its use, he said. "It's hard to know whether this increases the (total) number of abortions."