Cheryl Martin (Host): During the IVF process, there are many reasons patients and their physicians may choose not to do a fresh embryo transfer. Dr. Mary Hinckley, the IVF Medical Director at the Reproductive Science Center of the San Francisco Bay Area, is here to answer some of the top questions about the alternative, frozen embryo transfers or FETs.

This is Fertile Edge, a podcast from the Reproductive Science Center of the San Francisco Bay Area. I'm Cheryl Martin. Dr. Hinckley, it's great to have you on again.

Mary Hinckley, MD: Thank you so much for being able to speak with me today about this very important topic that so many patients ask about.

Host: So, let's talk about, you mentioned this as an alternative, what is a frozen embryo transfer or FET.

Mary Hinckley, MD: So, a frozen embryo transfer really refers to the cycle in which we will take the embryo that has previously been frozen, warm it, and put it back into a woman's uterus in order to create a pregnancy and hopefully a healthy baby. We do this for a number of reasons. Sometimes we will have frozen them, because people wanted genetic testing on them and most genetic testing requires us to freeze them while we wait for the answers. Sometimes we will do this because patients have extra embryos that they didn't use after a fresh transfer. And sometimes patients will do this, because they've frozen embryos for the future, and now they're finally coming back for them.

Host: And here's another question. When can I do an FET cycle?

Mary Hinckley, MD: Well, in our clinic, we allow patients to do their frozen embryo transfers shortly after the egg retrieval. So in most situations, patients will have an egg retrieval. And then, they may have their period six days or 14 days later. At that point, we allow them to go right into a frozen embryo transfer. Now, if they're still waiting for testing, or if they need to do a tune up of their uterus, or maybe get their blood sugars in control, or lose a few extra pounds before they get pregnant, all of those goals people have, we'll let them take a break, because once an embryo's been frozen, it can stay frozen forever, as long as there's liquid nitrogen in the tank. It does not degrade over time. But most patients will come back and do it when they're ready to be pregnant. And that's the beauty of splitting an IVF cycle in one part, that is the egg retrieval and embryo creation. And then, in the second part, that is the frozen embryo transfer, or the time in which we put it back.

Host: So, what are the success rates for frozen embryo transfers?

Mary Hinckley, MD: Well, it very much depends on where the embryos were created, what the IVF lab statistics are for that specific clinic. There are some generalizable statistics that we can use across the U.S. And most clinics will have a success rate of around 40-50% for a single frozen embryo. However, if a woman is older when they've frozen that embryo, the success rates could be lower, more like 15% if they're 40. Or if they're younger, the success rates could be higher, like 70%. If a patient ended up doing testing on their embryo and we know that it's chromosomally normal, in our clinic, the statistics are almost 69% of a live birth per chromosomally normal embryo transferred in a given month. And we almost always just put one in. With statistics and success rates like that, we want someone to have one healthy baby at a time and not have complications that can come from twins.

Host: Talk about the benefits of frozen embryo transfers over a fresh cycle.

Mary Hinckley, MD: Well, there are lots of benefits. And in my mind, I think patients can come into it in a more calm, relaxed way with the focus on their uterus and on their body supporting and growing that embryo. Many times, the benefit of doing it is that you get the genetic testing. In our clinic, a lot of patients choose to do PGT-A, which stands for pre-implantation genetic testing for aneuploidy, to make sure the embryo we're putting back has the highest chance of working and the lowest chance of miscarriage.

Another reason patients might choose to do a frozen embryo transfer is because there's less medication involved than in the fresh transfer when they've stimulated their ovaries and then they have extra hormones to help give luteal support or progesterone support. So in a frozen transfer, there's modifications we can make so that the medicines are less. There's less risk of ovarian hyperstimulation, which is that dreaded complication that people hear about with a fresh transfer. Although that risk is very small, even in a fresh transfer, it does not exist in a frozen transfer. And then, some patients choose to do the frozen transfer. And the benefit is that they can be at a time in their life when they're ready to have children, they have a supportive partner or family around them. And so, they can just choose the best time rather than forcing it at the time when their eggs might need to be frozen and embryos might need to be created.

Host: That's great. Anything else you want to add on this topic just on frozen embryo transfers?

Mary Hinckley, MD: Yeah. I'm glad you asked, because one of the questions I get asked frequently is which type of frozen transfer is best and many patients will hear, online or Google or TikTok, about the different types and there's really two main types. One is called programmed, people also call it controlled or medicated, and the other is called natural. And sometimes the term is modified natural.

Natural sounds so good. Most patients want that. But really, natural in our clinic just means you're naturally ovulating. You're still going to take some medicines and you're still going to have monitoring, whereas a programmed or controlled means we are not allowing you to ovulate. We are going to control your uterine lining and control the progesterone exposure so that we can fine tune it and have the most control to put that embryo in the most ideal situation. Patients say, "Which one's better, Dr. Hinckley? I'll do whatever you say." And in our data at our clinic, the implantation rate is not statistically different. We've been doing program cycles longer and the average patient tends to do program cycles and that implantation rate is around 77%. That sounds great with a chromosomally normal embryo.

And in the modified natural, which is what we do at our clinic, the success rate is about 75% for implantation. But that 2% difference, that's not statistically significant. So really, they're equally successful. However, some patients can't do a modified natural. They don't ovulate or maybe they've already gone through menopause. So, they have to do controlled. Some patients might have recurrent miscarriage and progesterone might be a problem. And so, they really want that progesterone to be ideal and optimized. And in a controlled cycle, we use injectable progesterone. It goes in the gluteal muscle. And so, that is more uncomfortable, because it is a shot that most patients take each night, but that gives more support. Some patients, that alone scares them. And they say, "No way am I going to do shots every night for six weeks. I'm going to do the modified natural where I only use a vaginal suppository for progesterone." So oftentimes, I can talk to patients about the two options. I can reassure them that they can both be successful if they are the type of patient that we would recommend both for and help them choose the one that's right for them, that has the right amount of monitoring, the right dates, whether they need to choose their physician, they want their physician to be there for the transfer. Programmed and controlled is sometimes better, because we have more control over that. But I can talk them through the pros and cons of each and assure them that they can have the best chances with the frozen embryo transfer.

Host: That's great personalized, individualized care. Thank you so much, Dr. Mary Hinckley, for addressing some of the most frequently asked questions about frozen embryo transfers or FETs. You can call 888-377-4482 to learn more and schedule an appointment with a RSC Bay Fertility Specialist. If you found this podcast helpful, please share it on your social channels and be sure to check out our podcast library for other topics of interest to you. This is Fertile Edge, a podcast from the Reproductive Science Center of the San Francisco Bay Area. Thanks for listening.