Answer from: Melvin H. Thornton, Associate Professor
First, let’s talk about two processes. Number one is preparing the uterus to allow the potential embryo to implant. Those medications are pretty straightforward. It’s designed to mimic a natural menstrual cycle. So in a natural menstrual cycle, the first part of a woman’s cycle, she makes a hormone called estrogen. What estrogen does is build up the lining of the uterus to allow for the embryo to implant. And then when she ovulates, she makes a hormone called progesterone. What progesterone does is provides nutrition for the embryo to grow into the placenta takes over about 8 to 10 weeks.
So when we’re preparing a woman’s uterus for receiving embryos after the eggs have been frozen, we want to give her these same natural medications that she makes in her body; we give her estrogen to build the lining of the uterus up. Estrogen can be given in pill form, patch form, or injectable form. Then once your lining is nice and thick, the thickness depends upon the individual doctor. But typically, anything over seven millimeters is thick enough to allow an embryo to implant. Once we see that the lining of the uterus is nice and thick, then she will start her progesterone, and the progesterone is either given in an injectable form or vaginal capsules. Sometimes very rarely can use oral medication for the progesterone, but typically after you start the progesterone, the embryos are transferred 5-6 days after you start the progesterone. Then both the estrogen and progesterone are maintained for the first part of the pregnancy.
Now, following the eggs, it’s important to understand that there’s a shell that surrounds the egg, it’s called the Zona Pellucida. And that can get very thick. And the Zona Pellucide is very important because the sperm have to penetrate the Zona Pellucida in order to fertilize the egg. So a woman who’s frozen her eggs and we thawed the eggs out, that shell can be thickened so the egg has to undergo a procedure called Intracytoplasmic Sperm Injection, where we take one sperm either partner sperm or donor sperm, and we inject that one sperm directly into the egg to bypass the hardening of the shell to get the egg to fertilize.
Once that egg is fertilized, we let it developed either to what’s called a day 3 embryo stage and is transmitted at that stage or the blastocyst stage which is a day 5 or day 6-stage embryo, and then the embryo is transferred at that point in time. The process of thawing and creating embryos is very straightforward. If you have a good-quality egg that was frozen, you can pretty much predict the survival rates to about 90%. Fertilization rate is anywhere between 80 to 90% as well with the intracytoplasmic sperm injection technique. Then if you’re younger, you have a very good chance of developing a blastocyst and good quality embryo. The randomized trials looking at pregnancy rates of frozen eggs are very good for young, healthy women. But as women get older, the pregnancy rates do decline because of the age of the egg that was frozen. So the younger the egg that was frozen, the better chance you have at a successful pregnancy in the future.
Answer from: Ioannis Zervomanolakis, PhD
We have the possibility of storing the eggs frozen for a longer time. As soon as the patient decides to use them, then we thaw them in the lab, and we use the sperm of her partner or sperm from a sperm bank in case if the woman is a single mother. Then we leave the embryos being cultured in the lab. So this is a very normal procedure that we use without any risk of damage to the eggs.
Can I use my frozen eggs for another cycle?
Egg freezing, also known as oocyte cryopreservation, is a way to save and store eggs safely at the clinic for future use. All eggs that have been collected from your ovaries can be frozen and then stored for later use. Your frozen oocytes can later be thawed, fertilized and transferred to your uterus.