Over the last decade, vitrification of oocytes has enabled the development of efficient fertility preservation programmes, providing increasing guarantees for women whose ovarian reserve, and therefore their reproductive capacity, may be compromised due to various reasons. This is the case for women with endometriosis, a population group representing 10% of women of childbearing age, who, because of this disease, will often need to undergo reproductive treatments to achieve their desire to become mothers.

It is clear that the number of vitrified oocytes and the age of the patient are key factors for reproductive success. But what is the appropriate number of oocytes to vitrify to optimise the chances of success?

This question gives rise to the study Number needed to freeze: cumulative live birth rate after fertility preservation in women with endometriosis, led by Dr. Ana Cobo, Director of IVI's Cryopreservation Unit, which shows that the higher the patient’s number of oocytes the greater her chances of success. Thus, in patients under 35 years of age with endometriosis, a 95% success rate was achieved, retrieving approximately 20 oocytes, while the maximum new-born rate was close to 80% in patients over 35 years of age.

“This was already known for women undergoing elective fertility preservation and cancer patients, but this information was not available for patients with endometriosis, where the question becomes even more relevant because these women have a higher risk of premature depletion of ovarian reserve. This research aims to help fertility specialists and  endometriosis patients set realistic expectations about their chances of reproductive success based on their vitrified oocytes”, explained Dr. Cobo.

The study includes data from 485 women with endometriosis who preserved their fertility between January 2007 and July 2018 at IVI's clinics in Spain, and who subsequently tried to become pregnant.

“These findings clearly indicate the beneficial effect of youth on reproductive outcomes in women with endometriosis who have preserved their fertility; however, special attention should be paid to women with advanced stages of the disease or who have required surgical treatment. While it is true that obtaining a maximum number of 15-20 oocytes for vitrification (probably in two cycles of stimulation) is relatively easy in young women, this may be more difficult in a patient with a compromised ovarian reserve, which may even be aggravated if the patient has undergone surgery”, said Dr. Cobo.

In this regard, a previous study, also led by Dr. Cobo, showed that young women achieved better outcomes when they had oocytes vitrified to preserve fertility prior to surgical removal of the ovarian endometrioma.

“This study shows that surgery has a quantitative effect on ovarian reserve, as the number of oocytes retrieved after surgery will be lower, which may have a negative impact on future chances of achieving pregnancy”, explained Dr. Cobo.

This study is key to physician-patient advice and is a very useful tool in the care of women with endometriosis.