Despite concerns that fertility treatments increase a woman's risk of developing breast cancer, a long term research finds no danger.

Nearly 10,000 women who received drugs to stimulate ovulation were no more likely to develop breast cancer during 30 years of follow-up than those who never used the drugs, researchers report on Fox News channel.

Previous studies have raised concerns over the drugs because women are exposed to higher levels of estrogen during fertility treatments. Extended exposure to extra estrogen could increase the risk of breast cancer.

"The other worry is that (these drugs) cause increased ovulation and . . . that could be linked to an increase in breast cancer risk," said lead author Louise Brinton, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute in Bethesda.

About 38 percent of the study participants were exposed to the fertility drug clomiphene and about 10 percent were exposed to drugs known as gonadotropins.

Over the three-decades of follow-up, 749 breast cancers were diagnosed among the study participants.

Overall, women who were exposed to either type of fertility drug were no more likely to develop breast cancer than those who didn't use the medicines to stimulate ovulation.

The researchers did find an increased risk of breast cancer among a small subset of women who were prescribed the highest doses of clomiphene, however.

Some of that increased risk may be the result of whatever underlying problem caused those women's persistent infertility, the researchers speculate.