(The Associated Press) - A new study has exonerated the IUD, the birth control device that has been shunned in the United States since the 1970s because of fears it makes women sterile.

The federally funded study found that never-pregnant women who had used a modern intrauterine device had no increased risk of their fallopian tubes becoming blocked.

"The IUD is much safer than previously thought," said David Hubacher, lead researcher and an epidemiologist at Family Health International of Durham, N.C., a nonprofit research group.

The study does not clear the Dalkon Shield, which started the IUD scare in the 1970s. Unlike other IUDs, it had multiple filaments that dangled from the device to let women know it was in the correct position. Doctors believe the filaments let bacteria climb easily into the uterus. The Dalkon Shield was not studied in this latest research and was taken off the market long ago.

Previous safety studies on IUDs had conflicting results. Many linking the devices and infertility had no comparison group, or they compared IUD users with women whose birth control method protected against sexually transmitted diseases. And chlamydia, one such disease, is known to be a major cause of infertility.

The latest study was conducted in Mexico, where IUDs are widely accepted, and was funded by the National Institutes of Health and U.S. Agency for International Development. It was reported in the New England Journal of Medicine.

Dr. Felicia Stewart, co-director of the Center for Reproductive Health Research and Policy at University of California at San Francisco, said the results are solid and part of "a gradually building consensus" IUDs do not cause infertility.

She called them a good option for women who are in monogamous relationships and thereby run a low risk of sexually transmitted infections. But she said women should consider condom use, choose partners wisely and get tested for chlamydia.

Dr. Gerson Weiss, chairman of obstetrics, gynecology and women's health at the University of Medicine and Dentistry of New Jersey in Newark, said he is not ready to clear IUDs.

"What this really says is, it's not a major issue," he said. The copper IUD, a T-shaped piece of plastic wrapped in copper wire, slowly releases copper, preventing pregnancy by irritating the uterine lining and altering fluid in the uterus and fallopian tubes. Some new versions release contraceptive hormones.

IUDs are 99 percent effective and last 10 years. They cost about $350, including the insertion procedure.

About 4 million Dalkon Shields were sold from 1971 through 1974, when U.S. sales were halted because the design was blamed for painful, sexually transmitted uterine infections resulting in infertility, hysterectomies, ectopic pregnancies and at least 18 deaths.

Manufacturer A.H. Robins & Co. of Richmond, Va., was deluged with lawsuits, filed for bankruptcy protection in 1985, set up a trust fund for injury claims and eventually paid about $3 billion to some 200,000 women.

Meanwhile, IUD use fell from nearly 10 percent to about 1 percent of the U.S. contraceptive market today. Yet with 106 million users, IUDs are the world's most prevalent reversible contraception.

Hubacher's group studied 1,895 women at three Mexico City public hospitals from 1997 to 1999. Nearly two-thirds were there seeking infertility treatment; the rest were pregnant for the first time. Some had used IUDs, some never did.

The infertile women were X-rayed to determine whether their fallopian tubes were blocked. Studying factors such as past birth control use and previous genital infections, the researchers found that IUDs were not associated with blocked tubes.

Weiss said younger doctors seeing the results will probably recommend the device to patients.

"An older doctor who was putting IUDs in in the '70s and had run into problems would still remember and say, "I don't want to put a woman through it,"' he said.

Copyright 2001 The Associated Press. All rights reserved.