This post was reviewed for medical accuracy by Rosalie Gunson, a Certified Registered Nurse Practitioner specializing in fertility care.
Ideally, you want to be as healthy as possible during IVF. That means all the usual things: staying hydrated, taking your vitamins, eating balanced meals, getting your flu shot, etc.
But what if you’re planning to do a frozen embryo transfer (FET) and you think you’re getting sick? Will your transfer be cancelled?
If you’re not feeling well but you don’t have a fever, you’ll probably be able to move ahead with a frozen embryo transfer (FET). But as always, it’s best to tell your fertility team about any symptoms you notice or medications you’re taking.
Let’s back up a minute and review the whole FET concept.
Why frozen embryos are used
In a “fresh” IVF cycle, you would take hormones to stimulate your ovaries. Your eggs would be retrieved and fertilized outside the womb. A few days later, the strongest and most promising embryo(s) would be transferred back to your uterus.
In a frozen embryo transfer (FET), the retrieval and fertilization happened in a previous cycle. The embryo(s) could have been frozen months or even years ago! The technology to flash-freeze embryos has gotten much better, so it’s being done more and more.
Why do people freeze embryos? Sometimes it’s because they did an IVF egg retrieval but had “too many” viable embryos to use in the same cycle. Most REs don’t recommend transferring more than one or two at a time, for fear of creating the next Octomom.
According to Shady Grove Fertility, having “spare” embryos from a previous IVF cycle is pretty common: “About 40 percent of patients who undergo IVF have an additional embryo(s) that they choose to cryopreserve (freeze) to use for another attempt, should their first cycle be unsuccessful, or to continue to build their family at a later date.” (Citation)
If you know you’re going to do genetic testing, that’s another reason to use frozen embryos. The trend is actually moving toward “freeze-all” cycles in which all embryos are tested and frozen — no fresh transfer is even planned. Then, a genetically normal embryo is transferred in a future cycle when the endometrial lining is ideal.
Onco-fertility preservation is another reason for freezing embryos. A cancer patient might freeze embryos before undergoing radiation so she can hopefully have a child once she’s in remission.
I should clarify that it’s also possible to freeze unfertilized eggs, but with FET we’re talking about transferring frozen embryos. Compared to frozen eggs, frozen embryos tend to be stronger and more likely to hold up during the freezing and thawing process.
Advantages of transferring frozen embryos
FET cycles have slightly higher pregnancy rates than fresh IVF cycles do. One explanation is that in a frozen cycle, you can delay the transfer until the lining is perfect.
For example, if your lining is only 6mm, you can take estrogen for another week and hopefully do the transfer when your lining is more like 8mm. In a fresh transfer, the timing is based more on when the embryo has reached blastocyst stage (Day 5 or Day 6).
Compared to a fresh IVF cycle, a cycle with frozen embryos usually involves fewer medications and fewer ultrasounds. That makes it significantly more affordable.
To prepare for a FET you’d likely take medications to build your endometrium, but you may not need to take stimulation meds or a trigger shot. It depends on which FET protocol you are doing. I’ll go into that in more detail in a minute. (For more about the importance of a good endometrial lining for implantation and pregnancy, see this post.)
Assuming that you are using your own embryos rather than donated embryos, you’d have at least one period between the retrieval and the transfer.
In other words, the transfer would happen in a new menstrual cycle. That gives your body a break after the hormonal onslaught of the stimulation process. Some studies have indicated that this can make the uterus “calmer” and more receptive to implantation.
Many women feel that a FET is less stressful than a fresh cycle because so many of the variables have already been controlled. When you already have at least one viable embryo, you don’t have to worry about the potential pitfalls in the earlier steps of IVF, like not getting enough mature follicles for retrieval or not having enough fertilized eggs develop into genetically normal blastocysts.
Also, if you’re lucky enough to have good frozen embryos available from a previous cycle, it’s nice to be able to use them. Otherwise, you’d have to keep storing them indefinitely (which gets expensive), or make the decision to donate or destroy them.
A Chinese study published in the New England Journal of Medicine in 2016 found that women with PCOS had better outcomes with frozen transfers compared to fresh ones: “Among infertile women with the polycystic ovary syndrome, frozen-embryo transfer was associated with a higher rate of live birth, a lower risk of the ovarian hyperstimulation syndrome, and a higher risk of preeclampsia after the first transfer than was fresh-embryo transfer.” (Citation).
Types of FET protocols
Not all FET protocols are the same. There are actually three different types:
1) Natural FET cycles: This protocol can work if you have regular, predictable menstrual cycles. Hormone levels (E2, LH, P4) are checked daily. The FET date is determined based on the surge in LH and the drop in E2. Sometimes an HCG booster shot is given post-surge to help increase natural progesterone production.
2) Medicated/Programmed FET cycles: This protocol is used for patients who don’t regular cycles or have a specific date they want FET to fall on. You’d be put on birth control pills for 2-3 weeks, then told when to stop pills and come in for monitoring. You’d start estrogen daily.
After about 11-13 days on estrogen, you’d have an ultrasound to check your lining. Ideally it would be at least 8mm thick and trilaminar. When your lining is ready, you would would start progesterone and schedule the FET on day 6 of progesterone.
3) Stimulated FET cycles: This is the least common FET protocol, and it’s typically only done when women have trouble getting their endometrial lining thick enough (8+mm). In a stimulated cycle you would take injectable meds to stimulate your follicles, just like in an IUI cycle. As the follicles grow and natural estrogen rises, the lining should get thick on its own without taking estrogen. Once the lining is thick enough, you’d do a trigger shot (such as Ovidrel) and do the FET.
Programmed FET cycles are popular at large clinics, partly for scheduling reasons. They don’t want their lab to get slammed with too many patients doing their FETs on the same day. Smaller clinics tend to do more natural cycles, but again, only for patients that have regular cycles.
What if you get sick before the FET?
Most REs won’t cancel a FET just because you’re not feeling your best, but they will check for a fever. If your temperature is over their cut-off (101 degrees, for instance), they won’t proceed with the transfer.
What’s the big deal about fevers? Generally, doctors will postpone any type of non-emergency medical procedure if you have a high enough fever, since it means you could have an active infection.
In addition, a high body temperature can interfere with implantation or proper fetal development. This is the same reason that women are advised to avoid hot tubs in early pregnancy.
For anybody doing fertility treatment but not a FET, I’ll add that a high fever isn’t good for the male partner’s fertility, either — it can affect sperm production.
As long as you don’t have a fever, though, minor symptoms like a stuffy nose or a sore throat during an IVF cycle or before your FET are probably no big deal and will not affect your chances of a successful conception.
Just remember that your options for medication will limited, since you can’t take anything that’s considered unsafe in pregnancy. You might have to suffer through a bad headache that Tylenol doesn’t touch, but at least you can continue with the cycle as planned!
If you get seriously sick before your scheduled FET but after you’ve started taking progesterone, your fertility clinic will probably cancel the FET rather than push the date back. That’s because progesterone can affect your endometrial lining.
Other reasons for cancelling cycles are covered in more detail in the post Why Would a Cycle of Fertility Treatment Get Cancelled?
What if you get sick after the FET?
Having a minor illness during the two-week wait shouldn’t have any impact on the potential pregnancy.
As with any medical procedure, though, there is a small risk of infection after an embryo transfer. Tell your doctor if you run a fever, start vomiting, or experience abdominal pain beyond a little cramping afterward.
Keep in mind that a slightly elevated temperature (not an actual fever) after ovulation is totally normal. If your basal body temperature (the temperature of your body at rest, usually measured first thing in the morning) stays high past the point when your period is due, you could be headed for a BFP!
Tracking basal body temperature (BBT) is a common way of tracking fertility signs, both for TTC and for natural birth control. Taking your temperature once isn’t very meaningful, but tracking (or “charting,” using a line graph) your BBT at the same time every morning for weeks or months can be illuminating.
To do this, though, you’ll need a basal body thermometer (Amazon link) — a regular thermometer won’t be sensitive enough. I’ve included a great, easy-to-read BBT thermometer on my Infertility Starter Pack page.
If you’re already tracking your basal temps and you did have a fever at any point in this cycle, be sure to take that into account when you’re interpreting your chart.
How soon after your FET could you begin noticing early pregnancy symptoms?
The problem with feeling sick — nauseous, achy, light-headed, whatever — after the transfer is that you can easily convince yourself that it’s an early pregnancy symptom, and early pregnancy symptoms are notoriously ambiguous.
Most of the early pregnancy symptoms people talk about are actually symptoms of high progesterone. Unfortunately that doesn’t mean anything, because progesterone rises after ovulation even if you’re not pregnant.
To add to the confusion, your RE will probably want you taking extra progesterone in the 2WW — and into the first trimester if you’re pregnant.
So it’s really hard to say that any particular symptom you’re feeling is a pregnancy symptom rather than PMS. But if you still want to obsess, I discuss symptom spotting in the two-week wait in a separate post here.
How soon after your FET can you take a pregnancy test?
In a non-IVF cycle, a fertilized egg can take 6-12 days to implant in the uterine wall. Until that happens, you’re not pregnant and you won’t test positive on a pregnancy test.
When you do IVF, the embryo you’re transferring has a head start over a freshly fertilized egg for two reasons:
- It’s a bit further along in development.
In a fresh IVF cycle, embryos are usually transferred 5 days after fertilization. (The egg retrieval day itself is considered Day 0.)That may not sound like much, but embryos grow quickly! A Day 5 embryo is actually called a blastocyst, and it already contains hundreds of cells.Typically, the embryos used for FETs were frozen on Day 5-6. While it’s possible to freeze embryos earlier, waiting until Day 5 makes it easier to tell which ones are the strongest and healthiest. - It’s put directly into the uterus.
Usually, a fertilized egg has to travel to the uterus from the fallopian tubes. IVF involves transferring the embryo directly into the uterus, which is why it can work for women with damaged or blocked fallopian tubes.
So while implantation in a non-IVF cycle could take 6-12 days after fertilization, it should only take one or two days after an embryo is transferred in a fresh IVF cycle. If the embryo was frozen, implantation could take a little longer — more like 5 days after transfer.
It’s definitely possible to get a positive on a home pregnancy test as soon as 5 days after the transfer. Usually, though, your RE will have you come in for a beta (a blood pregnancy test) more like 7-10 days after the transfer, so the results will be more reliable.
More info about pregnancy tests can be found in Can Ovidrel Cause a False Positive on a Pregnancy Test? and Pregnancy Tests: Is it a BFN if the Second Line is Faint?
Conclusion
You’ll probably be able to do a frozen embryo transfer (FET) with a minor illness, as long as you don’t have a fever. If your FET does get cancelled, though, just remember that the embryo isn’t going anywhere. You can try again when you’re feeling better!
This post was last updated in March 2021.
I’m Jenn! Here I am with my beautiful twin boys. My pregnancy was possible thanks to fertility treatment for PCOS.
