One in three young cancer patients who underwent ovarian tissue transplants have successfully fallen pregnant, and no one has had their cancer return as a result, the most comprehensive study to date has found. Not only did the procedure give them the opportunity to have a child, it also allowed them to reverse the early menopause that can result from chemotherapy.

"We are saying for the first time we have a cohort of patients who definitely seem to benefit from this, and none of those women have had a cancer as a result of transplanting the tissue," one of the researchers, Claus Yding Andersen from the University Hospital of Copenhagen in Denmark, told Sarah Boseley at The Guardian.

Andersen and her team conducted 53 ovarian tissue transplants on 41 young cancer patients between 2003 and 2014, 32 of which wanted to become pregnant. According to the study, which has been published in the journal Human Reproduction, one in three of these woman had successful pregnancies - half via IVF, and half naturally - resulting in a total of 14 babies between them.

"Of course, if you have a cancer as a young woman, all of them say 'I would like to survive', but immediately after that most of them say 'is it possible to preserve my fertility?' It is a huge issue for the patients," says Andersen.

Ovarian tissue transplants might seem like a novelty, but while doctors have been reluctant to perform the procedure in most parts of the world, in Denmark, young women with cancer are routinely given the option to have an ovary removed, frozen, and transplanted back once they’ve been cleared - free of charge.

The transplant process involves taking part of the removed ovary and cutting it into several small pieces before it’s frozen for safe-keeping. Once the cancer patient is cleared, these pieces are thawed and inserted into the tissue of the remaining ovary. This kicks the remaining ovary back into gear, restarting the process of ovulation in about four to five months.

In some cases, the Associated Press reports, the transplanted tissue lasted for up to 10 years, which is much longer than the scientists had predicted.

The reason the procedure has been so controversial is that doctors are concerned that by transplanting the tissue back into the cancer patient, they could be risking a recurrence. But the results of this study show that none of the 41 women experienced a return of their cancer as a result of the procedure.

Of the women who weren’t interested in falling pregnant at the time of the transplant, they were given the benefit of reversing the early menopause that was brought on by their cancer treatment.

The success of the procedure points to the possibility of all kinds of women - not just cancer patients - undergoing ovarian tissue transplants in the future. While Andersen is reluctant to comment on it, there is the possibility of young women having an ovary removed if they want to postpone having a child due to relationship or career restraints - without the anxiety of the looming biological clock.

It also points to the possibility of anyone who has to undergo chemotherapy being given the option to effectively preserve their fertility. "Chemotherapy treatment can cause infertility - a massive worry for thousands of younger women with breast cancer," Grete Brauten-Smith, clinical nurse specialist at Breast Cancer Care in the UK, told Boseley at The Guardian. "This could, in future, offer another valuable option for those who face the devastating prospect of not being able to start or add to their family."