Why We Sometimes Have to Freeze All Embryos
By Francis Polansky, M.D.
Most In Vitro Fertilization patients will have one or more “fresh” (unfrozen) embryos available for transfer inside their uterus.
There are five conditions when transferring “fresh” embryos would be unlikely to result in a successful treatment outcome.
Under these circumstances, all normally developing embryos will have to be cryopreserved (vitrified), and a Frozen Embryo Transfer procedure will be done at a later date.
- Slow embryonic development
Embryos should reach the blastocyst stage in five days. If it takes six or seven days, it is still possible to successfully conceive with them, but their development is now out of synchrony with the development of the endometrial lining.
- High estrogen level
If during ovarian stimulation estrogen level reaches 3,000 pg/ml or more, the development of the endometrial lining is accelerated and is becoming desynchronized with the embryonic development.
- High progesterone level
If during ovarian stimulation progesterone level becomes 1.5 ng/ml or higher, the endometrial lining undergoes premature secretory transformation resulting in desynchronization with the embryonic development.
- Thin endometrial lining
If, by the end of IVF ovarian stimulation, the endometrial lining thickness is less than 10 mm, the lining has become desynchronized with embryonic development and may not support normal implantation.
- Too many developing ovarian follicles
If during ovarian stimulation your ovaries develop fifteen or more follicles 15 mm in diameter or greater, the risk of severe ovarian hyperstimulation becomes too high if you become pregnant. Production of the pregnancy hormone HCG by an implanted embryo increases the likelihood, duration, and severity of ovarian hyperstimulation symptoms.
Embryo cryopreservation, thawing, and Frozen Embryo Transfer are very common procedures. Hundreds of thousands of babies have been born worldwide from cryopreserved embryos. The implantation rate of vitrified-thawed embryos is equal to the "fresh" embryo implantation rate, and there is no indication of any increase in the rate of birth defects.