Vitrification and Cryopreservation
The prospect of storing gametes, whether they are eggs or embryos, was until recently, good in theory but not great in practice. The method of freezing that has been used for the last 25 years resulted in the loss of up to 30% of gametes and also produced eggs or embryos that were significantly devitalized by the process. As a result, a frozen transfer was always a bonus but the success rates were lower than a fresh transfer.
This all changed over the last six to ten years with the development of the ultra rapid cryopreservation method called vitrification, developed and perfected in Japan.
With the introduction of vitrification, the survival rates for both eggs and embryos has risen to over 95% and the resulting gametes appear to be almost as good as they were in the fresh state. This single innovation allows us to consider the option of banking either eggs or embryos without compromising success when these gametes are ultimately used.
In IVF centers with access to advanced laboratory facilities and vitrification, frozen embryo transfer procedures now yield the same or even better success rates compared with the transfer of fresh embryos when the egg provider has herself been stimulated and undergone egg retrieval.
The Success Rate of IVF Delayed Transfer
As the success rate with frozen/thawed embryos approaches and surpasses the pregnancy rate in fresh cycles, more and more cycles of conventional IVF where a woman provides the eggs and carries the embryos herself, will now become cycles where embryos are banked by vitrification. The patient then returns the following month for a frozen embryo transfer. This embryo transfer is conducted either with natural ovulation, if this is predictable, or with a controlled frozen transfer where natural estrogen and progesterone is supplied in sequence allowing for a planned frozen embryo transfer.
Experts from Aberdeen University reviewed 11 previous studies, which followed to birth, more than 37,000 pregnancies resulting from the transfer of either fresh or frozen thawed embryos. When frozen embryos were used, there was a 30% lower risk of bleeding during pregnancy, 30 to 40 percent less chance of the baby being born underweight, 20% lower chance of premature delivery and 20% less likelihood of dying in the neonatal period. The study by Dr. Abha Maheshwari at the Aberdeen University was published in the journal, Fertility and Sterility, and was presented at the British Science Festival in Aberdeen in 2012. Dr. Maheshwari said: “We found pregnancies arising from the transfer of frozen thawed embryos seem to have better outcomes both for mothers and babies when compared to those after fresh embryo transfer.”
“If pregnancy rates are equal and outcomes in pregnancies are better, our results question whether one should consider freezing all embryos and transfer them at a later date, rather than transferring fresh embryos,” Maheshwari said.
At Zouves Fertility Center, we have been monitoring our pregnancy rates in fresh and frozen transfers when a woman provides the eggs herself. We noticed a steady increase in the success rates in the frozen transfers over the last three years, and for the first time, in the first six months of 2012, frozen success rates surpassed fresh pregnancy rates. This is due mainly to the benefits of vitrification, which we do across the board for all gametes in our program. Knowing that the pregnancy rates are higher in the frozen cycle and also when looking at the data from Europe, showing improved pregnancy outcome in frozen transfers versus fresh, it is a logical progression to stop doing fresh embryo transfer when a woman has been stimulated and rather to vitrify the embryos and transfer them during a future non-stimulated cycle.
Options for Embryo Transfer
The options for transferring the frozen embryos back to the uterus include the following:
- Natural frozen embryo transfer- where the patient tracks her ovulation and once the LH surge has been identified on urine testing, blood work and an ultrasound scan are performed confirming the LH surge as well as an optimal triple pattern on the endometrial lining and the presence of a dominant follicle in the ovary. The embryos are then transferred approximately one week later given that embryos are generally stored on day five or six after fertilization.
- Controlled frozen embryo transfer -does not rely on natural ovulation and the natural hormones. Estrogen and progesterone are added in sequence, thereby preparing a lining of the uterus, which is not dependent upon hormones from the ovary. The controlled frozen transfer is more suitable when patients live far away from the clinic or in patients where the ovulation is unpredictable.
Learn More about IVF Delayed Transfer
To learn more about IVF Delayed Transfer and vitrification, contact the Zouves Fertility Center. We are here to answer all of your questions about the procedure and help you identify the best possible ways to conceive a child.
Vitrification allows for women to preserve their embryos for years without having to worry about biological clock timing. Contact our fertility experts at Zouves Fertility Center to learn more about this revolutionary technology today.