Evaluating IVF Program Results
In 1989 Senator Ron Wyden introduced the in vitro fertilization (IVF) success bill requiring all IVF programs to report their results yearly to the CDC. The bill was intended to give couples meaningful data to make a treatment choice. While the bill was initially applauded there soon came the realization that programs were using the CDC statistics to promote their programs, i.e., programs were encouraged not to treat poor prognostic patients as well as to transfer high numbers of embryos. These practices produced better statistics, but also high levels of multiple pregnancies. Multiple pregnancies are associated with significantly increased maternal and fetal complications, some serious. Patient selection and number of embryos transferred is still the biggest difference in program success rates.
With the improvement of embryo culture systems, most IVF programs have moved from transferring cleaved, day 2 or 3 embryos to blastocyst, day 5 or 6 embryos with resultant higher pregnancy rates. With the higher implantation rates the American Society of Reproductive Medicine/Society of Assisted Reproductive Technology recommend transferring no more than two good quality embryos and in good prognostic patients, one. This practice has all but eliminated triplet pregnancies. There is still, however a high incidence of twins.
At the Florida Institute for Reproductive Medicine (FIRM) the chance of pregnancy with the transfer of one blastocyst embryo from a female 35 years or less is approximately 40%, with two embryos 60%. With the transfer of two embryos almost 30-40% of pregnant patients will have a twin pregnancy. The chance of an embryo splitting resulting in identical twins is approximately 2-3%. With the advent of pre-embryo genetic screening (PGS), whereby blastocyst embryos can be biopsied to see if they are chromosomally normal, pregnancy rates with a single blastocyst embryo are approximately 60%, with two approximately 80%. With the transfer of two PGS embryos the risk of a multiple pregnancy is approximately 50%. At the FIRM we recommend transferring only a single PGS embryo.
In order to evaluate chances for pregnancy it is necessary to assess how many eggs and the quality of eggs (ovarian reserve) likely to be obtained. The best guesstimates of ovarian reserve are anti-mullerian hormone level (AMH) a blood test, antral follicle count, an ultrasound assessment of the ovaries. The quality of eggs is largely a function of maternal age, but it also is influenced by number of eggs available. Age/ovarian reserve, give us the best guesstimate of the number and quality of blastocysts.
Another major breakthrough has been the improvement in embryo freezing using the vitrification technique. With the vitrification technique we have seen significantly increased embryo thaw/survival rates as well as ongoing pregnancy rates. Indeed pregnancy rates with vitrified blastocyst embryos mimic those for a fresh IVF cycle when estradiol levels are relatively low. In high response patients pregnancy rates are significantly higher using vitrified embryos transferred in a cryo replacement cycle where estradiol levels mimic those of nature. In high response patients fresh transfers have been shown to result in significantly decreased birth weights and higher instances of ovarian hyperstimulation syndrome. For these reasons, the FIRM is cryopreserving blastocyst embryos using the vitrification technique and transferring high response patients in a cryo cycle.
In summary, IVF best practices include:
- Transfer of blastocyst as opposed to cleaved embryos
- Freezing blastocysts using the vitrification technique
- Transferring high response patient in a cryo IVF cycle
- Transferring no more than two blastocyst embryos, one in good prognostic patients
- Strong consideration of pre-embryo genetic screening
- If a program is reporting inordinately high pregnancy rates be suspicious of the number of embryos transferred, in addition look at patient selection.