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.

Dr. Felicia Stewart, co-director of the Center for Reproductive Health Re-search 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.

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