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Frozen Embryo Transfers for More Successful IVF Cycles
With now over 3.5 million babies resulting from in vitro fertilization (IVF), constant attention to improving not only success rates of IVF but safety regarding the mother and fetus is paramount. Data now describe better obstetric and perinatal outcomes in pregnancies resulting from frozen embryo transfer (FET) cycles, when compared with fresh embryo transfers. In addition, success rates with frozen embryos are very similar to that with fresh embryos. This naturally raises the question of whether all embryos should be frozen and transferred at a later date. Is it time to retire fresh embryo transfer?
We theorize that the supraphysiologic (a dose that is larger or more potent that what occurs naturally; as in the resultant hormone levels after fertility drug treatment) estrogen levels achieved during stimulation for IVF may have a negative impact on the uterine lining. These levels are a necessary result of recruiting many eggs, which directly increases the success of an IVF cycle. Generally, the more eggs, the more embryos and the better the chance to find a healthy embryo.
It has always been a struggle to walk this fine line of wanting to give the patient the best chance for success, but trying to minimize the risk of Ovarian Hyperstimulation Syndrome (OHSS). In a cycle where all embryos would be frozen, the risk of OHSS would be greatly reduced for two reasons:
- The medication used for trigger of ovulation is different and greatly reduces the incidence of OHSS—to close to zero.
- The lack of pregnancy would typically reduce the length and severity of OHSS.
Furthermore, in pregnancies resulting from fresh cycles, some studies have shown correlation between the estrogen levels/numbers of eggs retrieved and the risk of antepartum (before birth) hemorrhage.
But cryopreservation (egg freezing) is not perfect either. Some embryos can be compromised from the freeze/thaw process. Some postulate that the more robust embryos will survive the process and be selected out that way. As practitioners, we desire a safe method where we can aggressively stimulate a patient to produce the most and best embryos (in order to maximize success rates) but also limit their risk for both OHSS and obstetric/perinatal morbidity. “Freeze-all” embryos cycles may accomplish this.
This type of cycle involves two phases: the first results in production of embryos and in the second, the uterine lining is prepared to receive thawed embryos. The time frame for completion of a cycle is longer than with a fresh transfer, and costs may be different. Certainly insurance coverage of FET cycles influences the expense to the patient with this scenario.
A recent publication by A. Maheshwari In Human Reproduction (November 2012) examined the data regarding this important question and determined that the scientific evidence to date does not support this change in practice across the board. However, larger trials may indicate that elective cryopreservation (egg freezing) is ultimately the best balance of success and safety. We look forward to seeing more of these data analyzed so that our fascinating and dynamic field can remain as effective as possible for our patients.