Researchers at the Brigham have developed a user-friendly counseling tool that estimates the number of eggs a woman should freeze based on her age and the number of children she wants to have in the future.

It is the first model to consider maternal age by individual year, versus age range, and to include how likely an embryo created with those eggs will have the correct number of chromosomes.

Janis Fox

“We wanted to create a tool that is evidence-based in order to provide the best possible guidance for our patients, who are making big decisions about their lives, their families and their finances,” said Janis Fox, MD, attending reproductive endocrinologist in the Center for Infertility and Reproductive Surgery and senior author of the paper describing this new model, which was published in Human Reproduction this month.

The American Society for Reproductive Medicine lifted the experimental status for egg freezing in October 2012. Since then, the popularity of the procedure has increased.

Developing Data-Driven Guidance

Although primarily intended for women whose fertility may be in jeopardy due to treatment for cancer or other illnesses, egg freezing has become an attractive option for women who are electively delaying childbearing. But, because this option is relatively new, and the majority of women who have frozen their eggs have not yet returned to use them, the likelihood of a frozen egg resulting in a healthy baby is largely unknown.

The procedure is also expensive. The majority of women who elect to have their eggs frozen face out-of-pocket costs of up to $6,000, excluding the cost of medications. That typically covers one egg-freezing cycle that, depending on individual circumstances, results in a variable number of eggs suitable for freezing.

Randi Goldman

It’s also not known how many frozen eggs are necessary to have a child in the future and what happens when a woman wants to have more than one child. These questions often leave a woman unsure of whether she should repeat a cycle in order to store more eggs and potentially increase her future chances of having a baby.

To address these issues, Fox and her colleagues looked at data from 520 healthy, fertile women undergoing in vitro fertilization. Researchers studied survival rates of thawed eggs, the percent of fertilized eggs that developed into healthy embryos and the number of healthy embryos needed to result in a live birth.

Their model found that a 35-year-old woman who freezes 10 eggs following her first cycle had a 69 percent chance of one live birth. If she undergoes a second cycle and now has 20 frozen eggs, the chances jump to 90 percent for one live birth. With 30 eggs, the likelihood of success rises to 97 percent.

Catherine Racowsky

“Rather than explicitly telling women how many eggs they should freeze or how many cycles they should undergo, we believe that our model will help women make informed choices based on the data that is available and on their family-building goals,” said Randi Goldman, MD, a Reproductive Endocrinology fellow in the Center for Infertility and Reproductive Surgery and first author of the paper. Catherine Racowsky, PhD, HCLP, director of BWH’s IVF Laboratory, also contributed to the study.

Researchers are developing a digital version of the tool that they hope to make available in the near future. They caution that the assumptions used to create the model, while data-driven, were based on outcomes from BWH and may vary by fertility center.