6 of 12

Fertility Preservation for Cancer Patients

Lesson 6 of 12

Factors That Impact Success

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Factors That Impact Success

As we alluded to in an earlier lesson, the odds that frozen eggs will lead to a live birth is often a function of three factors: the age of the person when eggs were frozen, the number of eggs frozen, and finally, and the quality of the laboratory freezing and thawing the eggs.


In this section, we’ll include data for patients freezing their eggs for "elective" purposes and those for oncological purposes. Our rationale to include both, and at times compare, is two-fold. For one, the sample sizes for the "elective" egg freezing group tend to be larger and when there are gaps in the cancer patient data (e.g. over the age of 40), having "elective" patient data can be useful. Second, most clinics will discuss success rates of their "elective" patients and so having a general basis of comparison is probably useful.

To start, below is data from a single clinic on how age seems to coincide with whether frozen eggs will work both for "elective" and "oncofertility" egg freezers.

Number of Eggs Frozen

As we mentioned, age in conjunction with the number of eggs frozen are two factors that often provide better resolution on whether an egg freezing cycle will work. Below is data from the same clinic but in a slightly larger study.

Investigators in this study noted that when “elective” and oncofertility patients had similar numbers of eggs retrieved, and once corrected for age disparities, rates of success were similar. To the extent oncofertility patients had fewer eggs retrieved may be a function of the stimulation protocol they were put on (e.g. less gonadotropin) and not necessarily reflection on how the cancer itself might impact ovarian function (a question experts are divided on.) A fair question for cancer patients to ask is whether the nature of their cancer necessitates they be put on a protocol that limits the amount of gonadotropin they receive. For instance, doctors may feel more comfortable prescribing higher doses of gonadotropin to a patient with a cancer less susceptible to swings in estrogen, thereby plausibly raising the number of eggs that will be retrieved.

As an aside, the extent to which the nature of the cancer itself (as opposed to the treatment of the cancer) impacts the number (or quality) of eggs produced remains largely unanswered. For instance, below are a handful of studies comparing egg yield in BRCA-positive and BRCA-negative cancer patients and non-cancer patients. In some studies, investigators noticed a distinction in egg yield and attributed it to the nature of the cancer. In other studies, investigators couldn’t detect any such difference.

Given the correlation between the number of eggs collected and the improving odds of success, patients might consider returning for a second egg retrieval. Here it’s probably worth considering a number of factors. First, we have no data on how a second retrieval impacts cancer treatment timelines (below) and how the additional volume of drug impacts the odds of cancer-free survival long term (both subjects we cover more in depth in the next chapter.)

Second, one likely needs to consider their family-building goals. The desire to have many children might sway a patient to more closely examine an additional retrieval. Third, the context of the number of eggs retrieved (and what an additional retrieval could yield) is relevant. As you can see in the data below, while doubling an egg count from 2 to 4 eggs may not dramatically raise the likelihood of success, going from 10 to 20 eggs may. Finally, and again, much of this needs to be considered in the context of each person’s odds of diminished fertility and in their level of comfort (or lack thereof) of those diminished odds.

Selecting a Clinic

Finally, a critical factor in the odds of whether frozen eggs will yield a delivery (if needed) is the quality of the laboratory handling both eggs and sperm. To illustrate why laboratory quality is important, below is data from two clinics within one mile of each other and their odds of IVF success when each uses eggs from donors (who are likely of similar good quality). As you can see, the difference in rates of success is nearly two-fold.

Freezing and thawing eggs is incredibly difficult, few clinics have much experience doing it, and so we think it’s critical to select the best laboratory to which you have access. To the extent you have the ability to get data from clinics themselves, we think it’s wise to focus on two numbers. The first would be a clinic’s "oocyte cryosurvival rate" or what percentage of frozen eggs are usable when thawed (80% is passable and 90% or better is exceptional.)

The second would be the “blastocyst conversion rate” or what percentage of fertilized eggs reach the “blastocyst” stage of embryo development (40% is passable, 60% or better is exceptional.) To the extent collecting information isn’t realistic, and your country has a database of clinical success rates (e.g. SART in the US), consulting and comparing success rate data from donor eggs (most donors are of comparable good quality—thereby removing the variable of who is seeing the harder-to-treat patients) can be a useful basis for comparison.

We have a detailed course here on what a laboratory does and other factors to consider, but for the sake of this discussion it’s also important your laboratory remains open seven days a week (so your retrieval happens when it’s best for your outcomes, not their schedule) and there is meaningful quality control and disaster recovery plans in place should a power outage or natural disaster occur.

While the clinic’s laboratory quality should be the primary factor in making a selection, there may be other factors to consider. One would be the degree to which they are coordinated with your oncologist and how commonly they see oncofertility patients—as you’ll see in a following lesson, there can be a lot of nuance to treating patients with a cancer diagnosis. Another factor would be the extent to which they make treatment financially accessible—either in so far as they accept your insurance (so long as you have coverage for the process) or are willing to discount services.