Oocyte (egg) Cryopreservation
A newer technology that is now available is freezing of womens’ eggs without fertilizing them first. This allows women to store their eggs for future use without ethical concerns if they should choose not to use them. Women who are single and would like to delay childbearing or for women with a medical condition that may affect their ability to conceive in the future (e.g. severe endometriosis, chemotherapy or radiation treatment for cancer) are good candidates. However, for these eggs to be viable in the future, they shoud be “good” when frozen. So, younger women, women who do not smoke cigarettes and women with normal ovarian reserve testing are ideal candidates. This is because the eggs are fragile and some will not survive thawing, others will not fertilize and many will be genetically abnormal.
Frozen Embryo Transfer
Embryos can be cryopreserved or frozen indefinitely. Because the embryos are kept in liquid nitrogen, they do not “age” or go bad. Embryos are usually cryopreserved on day 5 at the blastocyst stage. To prepare for a frozen embryo transfer, the woman’s uterus must be synchronized in development with the embryos. There are two ways to accomplish this:
- Take medication to control the cycle and plan for a transfer date that is convenient.
- Follow a woman’s natural cycle and proceed with the transfer.
Most of the time, women choose the first option so that the transfer date is conveniently scheduled in advance. This process is longer and usually takes about six weeks to prepare for the transfer. The schedule involves taking birth control pills for about three weeks starting at the beginning of the menstrual period. During the second week, a medicine called Lupron is started. This will help to prevent a woman from ovulating. Next, to thicken the uterine lining to support implantation of the embryos, estrogen tablets are prescribed. An ultrasound exam is performed to determine that the uterine lining has reached the appropriate thickness (this usually takes two weeks). Then, progesterone is started. Progesterone organizes and dates the uterine lining so that it is synchronized with the embryo development. At this point, the transfer date can be finalized.
Alternatively, a natural cycle involves fewer medications, but also makes scheduling more cumbersome. A woman should have regular ovulatory menstrual cycles if she chooses this option. Follicle monitoring, blood work and ultrasound exam, is performed a few days before the expected ovulation date. The uterine lining is assessed for the appropriate thickness and the development of a dominant follicle. Then, an injection of pregnancy hormone is administered to force the egg to ovulate. This also enables us to know exactly when ovulation has occurred. The embryo transfer date is then based on when the woman ovulates.