Clomifene is one fertility drug looked at by the researchers
Taking fertility drugs does not increase a woman's risk of developing ovarian cancer, a large Danish study has reported.
A study of 54,362 women referred to fertility clinics between 1963 and 1998 showed no overall increased risk of ovarian cancer for any IVF drug.
But the researchers say they will have to monitor all the women until they are older to be sure of the findings.
The findings appear in the British Medical Journal.
According to the researchers, there has been considerable debate over the past three decades as to whether use of fertility drugs increases a woman's risk of developing ovarian cancer.
Results from other studies have been conflicting and there were particular concerns about women who undergo several cycles of treatment or who never get pregnant.
In the study, of women who had been referred to all fertility clinics in Denmark, 156 developed ovarian cancer.
Over an average follow-up of 16 years, there was no increased ovarian cancer risk associated with four groups of fertility drugs looked at.
The researchers also found no increased risk among women who had undergone 10 or more cycles of treatment or among those who did not become pregnant.
However, there was a significant increase in risk of the most common serious type of ovarian cancer among women who had used the drug clomifene but the researchers said this was likely to be a chance association.
As many of of the study participants have not yet reached the age at which ovarian cancer becomes most common, the researchers will continue to monitor the risk of the women as they get older.
Dr Allen Jensen, study leader and researcher at the Danish Cancer Society, said in the 1990s two studies had suggested an increased risk of ovarian cancer with use of fertility drugs and research since had been inconsistent.
"Based on our present data, the results are reassuring," he said.
Professor Hani Gabra, director of the Ovarian Cancer Action Research Centre, Imperial College London, said: "This will be a huge relief to many women who have undergone fertility treatment.
"Currently, very little is known about the causes of ovarian cancer other than a relationship to ovulation, increased risk with age, a genetic predisposition in families with a history of breast and ovarian cancer, and being overweight all being important factors."
Dr Allan Pacey, fertility expert at Sheffield University and secretary of the British Fertility Society, said a potential risk of ovarian cancer was a common worry among women undergoing fertility treatment.
"This is a monumental long-term study and it is extremely reassuring," he said.
"There are a few caveats but this should put most people's minds at rest."
Liz Baker, senior science information officer at Cancer Research UK, said the research was good news.
"This large study reinforces previous research that found no significant link between fertility drugs and ovarian cancer.
"It's important to remember that increasing age is the biggest influence on the risk of this disease."