Benefits of Cryopreservation of Embryos
Embryo freezing adds an important dimension to assisted reproduction by:
- Extending the possibility for pregnancy if a fresh cycle is not successful or when couples desire additional children after a successful embryo transfer and delivery.
- Avoiding ethical dilemmas by eliminating the need to dispose of remaining embryos.
- Offering an alternative to couples that might transfer too many embryos and risk a multiple gestation pregnancy.
- Embryos are frozen individually for efficient future use.
Decreasing the Risk of Ovarian Hyperstimulation Syndrome (OHSS)
This advancement in the process of embryo cryopreservation has had a dramatic impact on our practice by lowering the risks for complications such as ovarian hyperstimulation syndrome (OHSS) or multiple births and improving the overall success rates for our patients. For example, it is now common practice to recommend embryo cryopreservation rather than a fresh embryo transfer to a patient who is hyper-responding to the ovarian stimulation protocol. Cancelling the fresh embryo transfer can significantly reduce the risk for developing OHSS especially if it is in conjunction with the use of the GnRH-agonist or Lupron trigger protocol. This is a way to trigger the final maturation of the eggs with a very low risk for OHSS; however, fresh embryo transfer pregnancy rates are typically low, therefore this is combined with embryo cryopreservation and a subsequent FET cycle.
Uterine Environment Concerns
Embryo cryopreservation is also commonly recommended in situations where there is a concern about a suboptimal uterine environment for implantation. This would include ultrasound evidence of inadequate endometrial thickness, development of endometrial fluid, premature elevation in blood progesterone hormone levels, or the unexpected finding of a uterine lesion (e.g. polyps or fibroids). Since there is little to no concern about a reduction in the potential for an embryo due to the freezing process, it is best to wait until the uterine environment can be optimized for implantation.
Preimplantation Genetic Diagnosis (PGD)
Following the same line of reasoning to achieve optimal uterine environment for transfer, we have modified our protocol for Preimplantation Genetic Diagnosis
(PGD) cycles. Previously the PGD protocol involved an embryo biopsy on day 5 (5 days after egg retrieval) with a possible fresh embryo transfer on day 6. We have seen higher pregnancy rates if we biopsy and freeze the embryos in one cycle and transfer in a subsequent FET cycle where we can optimize the synchronization between the embryo and the endometrium. Pregnancy rates with the “freeze all” protocol have been over 40% higher (fresh transfer clinical pregnancy rate per transfer 39% (27/70) vs. FET clinical pregnancy rate per transfer of 55% (62/113).
Elective Single Embryo Transfer (eSET)
Arguably the greatest impact of the new cryopreservation protocols has focused on the approach to the discussion about the number of embryos to transfer. Now that we are confident that for the most part, a fresh embryo and a frozen embryo cryopreserved with current protocols will have similar success rates, we encourage patients to consider the “one at a time” approach. In the scenario discussed earlier, a patient with two good quality embryos should not feel pressured to transfer both in a fresh cycle to maximize the potential for the embryo. The second embryo could be cryopreserved for a future FET cycle if the first single embryo transfer is not successful or for an attempt at another pregnancy in the future, if it is successful. In our clinic, this has led to a dramatic increase in acceptance of elective single embryo transfer (eSET). For 2013, GIVF’s eSET cases increased by 38% over 2012 for patients under the age of 35 using their own eggs in a fresh IVF cycle. Additionally, the number of eSET cases for donor egg/fresh embryos more than doubled in that time period.
As is the case in almost all medical issues, each patient is an individual with a unique set of circumstances. Therefore, one should not make a blanket statement that frozen embryos are better than fresh or vice a versa. However, there is confidence that current embryo freezing techniques maintain most if not all of the potential of an embryo to produce a pregnancy. This information can be used as part of the broader discussion to address the best course of action for each individual patient.