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Fertility, IVF and Egg Donation
Do IVF frozen embryo transfer (FET) cycles have increased success rates or other benefits as compared to fresh transfers?
Over the past several years there have been several studies published that investigated whether fresh or frozen transfers result in higher IVF pregnancy success rates and also which type of transfer is associated with healthier outcomes for mothers and babies.
In fact, some IVF programs have completely stopped doing fresh embryo transfers and are only performing frozen embryo transfers. As of now (summer 2016), the IVF field in the US seems to be slowly moving toward doing more frozen embryo transfers and less fresh transfers. This might be a long-term trend that could help us achieve the most successful treatment outcomes.
There are 2 general issues related to the possible superiority of frozen embryo transfer as compared to fresh transfer.
- The rate of implantation could be reduced in fresh transfers as compared to frozen embryo transfers.
- There could be a “healthier” implantation process in FET cycles with development of a better connection between the placenta and the mother. This could potentially result in benefits at multiple levels.
Over the last 10 years or so embryo freezing and thawing efficiency has improved dramatically with widespread use of vitrification (ultra-rapid freezing) vs. the older slow freezing method. This led to much better pregnancy success rates with frozen embryos than we saw in the past. Now some fertility specialists are claiming that frozen embryo transfers actually give higher success rates than fresh transfers.
Embryo implantation with a frozen cycle could be better with the more “natural” hormone environment in the uterus. The uterine lining in a fresh cycle with ovarian stimulation is exposed to unnaturally high levels of the reproductive hormones estrogen and progesterone which could deter effective embryo implantation.
Some of the studies done so far show significantly higher pregnancy rates with frozen embryo transfers as compared to fresh embryo transfers. However, other studies have shown no significant difference in success rates between fresh and frozen transfers.
One problem is that there are several variables that are difficult to control for in order to have the proper study design to answer this question. Overall, at this point the evidence suggests that frozen transfers seem to have somewhat higher pregnancy rates as compared to fresh transfers.
Further studies should be done to confirm (or deny) this and also to investigate whether there are subsets of patients that benefit more than others by having their transfer “deferred” to a frozen cycle. It is possible that some patients would get a large increase in their chances for pregnancy with an FET and others would get little or no benefit at all. We just don’t know enough yet.
For example, several studies that have shown that IVF patients that take a “pure” Lupron trigger (without any HCG trigger) have better pregnancy rates in an FET cycle vs. with fresh transfer. However, the magnitude of the difference is debatable and in many clinics (ours included) it is a relatively small percentage of the patients that get a pure Lupron trigger.
This issue is about ovarian hyperstimulation syndrome, OHSS. Mild ovarian hyperstimulation is fairly common with IVF and is not a major medical problem. It goes away fairly quickly and has no major consequences. However, severe OHSS is serious and needs to be avoided.
By utilizing a pure Lupron trigger (also called an agonist trigger) severe OHSS can be completely avoided. However, some IVF patients do not get a pure Lupron trigger (they took some HCG at trigger time) and these women might become significantly hyperstimulated if they become pregnant from a fresh embryo transfer. These women should have their embryos frozen and then later thawed and transferred (FET) after the hyperstimulated ovaries regress to normal.
Tubal pregnancy rates
There is some evidence from retrospective studies that ectopic pregnancies are more common after fresh as compared to frozen embryo transfers. For example, one study reported ectopic pregnancies occurring in 4.6% of clinical pregnancies after fresh transfers and 2.2% of clinical pregnancies after frozen transfers. Some other studies have shown smaller differences.
Obstetric and perinatal outcomes
So far, the studies on health outcomes for mothers and babies after fresh vs. frozen embryo transfers show mixed results. Overall, it seems that there might be more healthy outcomes after FET as compared to after a fresh transfer. However, more research is needed in this area. The list below summarizes results from some recent studies.
- The risk for a baby to have low birth weight is increased after fresh compared to frozen transfers (favors doing FET)
- The risk for having a preterm birth is increased after fresh compared to frozen transfers (favors doing FET).
- The risk for having placenta accreta (placenta attached deeply in uterine wall and difficult to separate at delivery) seems to be increased in frozen as compared to fresh embryo transfers (favors doing fresh transfer).
- The risk for having a large for gestational age baby seems to be increased in frozen as compared to fresh embryo transfers (favors doing fresh transfer).
There is some evidence that pregnancy rates are somewhat higher and overall outcomes may be better for pregnancies with frozen transfers compared to with fresh transfers. However, as discussed above, some of the outcome data shows pros and cons for FETs.
Other important questions are how much better will these outcomes be, and how much extra will it cost with switching from fresh embryo transfers to FETs? Then, couples (and their doctors) must decide whether that additional benefit is worth that extra cost.
That question will not have the same answer for every couple because financial resources and insurance coverage varies between couples. If patients have excellent insurance coverage that will pay for multiple cycles of fresh and frozen embryo transfers then the economic decision for a couple could be easy. However, few people have insurance coverage like that.
The debate about these issues continues in our field of medicine. There are important questions to answer and well designed studies are needed. In the meantime we try to make the best decisions with our patients on a case by case basis.
Welcome to the
Richard Sherbahn, MD is a Board Certified Reproductive Endocrinology and Infertility specialist.
Dr. Sherbahn founded the Advanced Fertility Center of Chicago in 1997.
He will post regularly about fertility issues.
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