IVF Outcome Definitions
Our professional society, SART (Society for Reproductive Technologies), and the CDC (Centers for Disease Control) initiated a new method of calculating IVF outcomes for 2014 and beyond.
The reasons for these changes reflect the changing practices of IVF centers and patients. In particular, the advent of reliable preimplantation genetic screening (PGS) of embryos led to patients undergoing multiple IVF cycles to accumulate a larger number of embryos before testing the embryos to identify the one with normal chromosomes. Thus, the embryo transfer (ET) often reflects the outcome from choosing the best embryo from a pooled group created from more than one cycle, which is not the same as the outcome from transferring the best embryo from a single cycle.
Additionally, we recognize that the cumulative livebirth rate from the transfer of both fresh and frozen embryos a single initiated IVF cycle is also an important statistic for patients. Previously, you could see the outcome of either fresh embryo transfers or frozen embryo transfers but the cumulative livebirth rate could not be calculated from the reported statistic since not everyone had any or the same number of embryo transfers.
Finally, we learned that PGS requires biopsy of embryos on blastocysts (Day 5/6 embryos) in order not to “harm” the embryo by causing a lower probability that it would implant and grow. Most IVF centers do not have the ability to run genetic testing in their own laboratories, so they have to ship the biopsied embryo cells to an outside lab for analysis. The woman’s uterus will not allow embryo implantation beyond about noon on day 6 after egg retrieval (window of implantation). Therefore, most IVF centers must freeze all the embryos and transfer them in the future during a frozen embryo transfer cycle (FET).
To address the change from fresh embryo transfer to many frozen embryo transfers; SART/CDC now considers the first embryo transfer to be the “primary” transfer, whether the embryo is fresh or frozen-thawed. Consequently, the concept of “Fresh ET” and “Frozen Embryo Transfer” is outdated. We now use “Primary ET” to refer to the first transfer after egg retrieval whether the embryo is fresh or frozen-thawed and “Secondary ET” to reflect all the other frozen-thawed ET.
What do the numbers mean now?
Statistics using Intended Egg Retrieval Cycles are helpful for patients before they begin a cycle because these statistics include everyone who gets cancelled or does not have a transfer. Thus, these statistics reflect the outcome of everyone who starts treatment, which some argue are the most helpful to patients because they include everyone who starts and not just the patients with a high probability of success.
IVF cycles are cancelled for many reasons but the most common is that the ovaries did not stimulate well and there would be few eggs to work with (low response).
1 Preliminary Cumulative Outcome per Intended Egg Retrieval: The percentage of cycles started with intention of having an egg retrieval that resulted in a livebirth from the cumulative efforts of both fresh and frozen-thawed embryos from a single egg retrieval. Importantly, this statistic includes all cycles started including those cancelled for any reason and those cycles where all embryos were frozen to “batch” with other cycles before ET.
2 Ongoing/Delivered Pregnancy/Transfer: The percentage of embryo transfers with an ultrasound-proven embryonic heart rate that did not miscarry. This percentage includes both ongoing pregnancies and those that we know have delivered, thus the statistic should be very close to the combined delivery rate that we report to SART and the CDC.
3 Implantation Rate: The percentage of embryos transferred that resulted in an ongoing pregnancy. We calculate this number by dividing the number of ongoing pregnancies by the number of embryos transferred. The implantation rate is a very good way to determine the embryo quality from the IVF lab. Note that we transfer so many single embryos that the implantation rate becomes an important measure of embryo quality.
4 Elective Single Embryo Transfer: The percentage of patients who chose to transfer a single embryo when they had multiple embryos available for transfer. We use this statistic to gauge how aggressively the clinic tries to avoid multiple gestations. Clinics with high implantation rates can perform more eSET and maintain a high pregnancy and delivery rate.
We use a Clinical Prognosis Score to help us inform patients regarding their chances for success with IVF. Not every patient has the same chance of becoming pregnant and our score provides a filter for success estimates.
The prognosis score derives from clinical/laboratory values/findings. We developed this scoring system about 10 years ago to help differentiate patients with variable fertility potential. While not as obvious in our initial smaller sample size (because we are doing so well in all groups!), the score previously stratified patients into significantly different outcome potentials.