IVF is mostly thought of as the fertilization of eggs and the growing of embryos outside
of the body in the IVF laboratory, but there are two procedures which involve the women
themselves.
Extracting eggs from the ovaries or egg retrieval and putting embryos into the uterus, which
is called an embryo transfer.
Every time a woman does an embryos transfer, she has a chance for pregnancy.
IVF success rates can be calculated by looking at the chance for success on a single embryo
transfer or after multiple embryo transfer attempts which is called the cumulative pregnancy
rate.
Is there an optimal number of eggs that could maximize the chance for pregnancy?
Stay tuned.
It makes sense that the more times you attempt pregnancy, the better your chances for ultimately
being successful.
In order to have multiple embryo transfer attempts, you of course must have multiple
embryos.
In order to have multiple embryos, you need to have multiple eggs.
The number of eggs that a woman produces with IVF depends on how well her ovaries respond
to fertility medications and the IVF protocol that the doctor chooses.
Some women may produce a lot of eggs and some women may produce very few.
Is there an optimal number of eggs that could maximize the chance for pregnancy?
It turns out that it depends on whether you are trying to maximize your chances on the
initial fresh embryo transfer or maximize your cumulative chances with additional frozen
embryo transfers.
Let’s talk about fresh embryo transfer first.
What is the optimal number of eggs to obtain in order to maximize the chance for pregnancy
in a fresh embryo transfer?
A number of studies have looked at this.
Recently, a large study looked at about 15,000 women undergoing their first IVF egg retrieval
in 15 different European IVF centers.
For the initial fresh embryo transfer, they found that the more eggs that are retrieved,
the higher the live birth pregnancy rate... until you reach about 7 eggs.
For a fresh transfer, getting more than 7 eggs didn’t seem to help.
The pregnancy rates stayed mostly the same between 7 and 20 eggs.
This generally agrees with previous studies using large IVF registries which found that
fresh transfer pregnancy rates increased until about 10 to 15 eggs were retrieved.
When more than 20 eggs were retrieved, the pregnancy rates for the fresh transfer became
lower.
This decrease is likely due to two factors.
In some cases, patients may have decided not to do a fresh embryo transfer and instead
froze all of their embryos to reduce the risk of developing OHSS.
In this study, these patients were recorded as being not pregnant from the fresh transfer.
In other cases, it may be due to adverse effects on the uterine lining which resulted from
the high hormone levels during the ovarian stimulation.
Remember, the more eggs that are retrieved in an IVF cycle, the higher the chances for
developing a complication called ovarian hyperstimulation syndrome or OHSS.
If you are not planning to freeze extra eggs or embryos, retrieving larger numbers of eggs
will increase your risk for developing OHSS and potentially reduce your chances for becoming
pregnant.
However, when you also consider doing frozen embryo transfers, then the results are different.
The European study found that when you include the live births that occurred after adding
in the frozen transfers, the more eggs that were retrieved, the higher the cumulative
chances for pregnancy.
This was true with younger patients who were 35 year old or less, intermediate ages between
35 and 40 and older patients who were greater than 40.
Amazingly, there did not seem to be an upper limit.
Cumulative pregnancy rates continued to improve as the number of eggs retrieved increased.
In the past, people have worried that an IVF protocol that produced a higher number or
eggs would produce eggs with poor quality.
The data from this study suggests that may not be true.
Couples that had more eggs retrieved ultimately were able to get more live births.
So a strategy in which you aim to try to get more embryos to freeze can increase the chances
for having a baby.
It may be possible to accomplish the same thing by doing several egg retrievals that
produce less eggs each time compared to a larger number of eggs at one time.
However, this is considerably more expensive than doing just one egg retrieval and of course
is a lot more invasive and uncomfortable for a woman to have to do multiple egg retrievals.
But if you are a woman who doesn’t respond well to fertility medications and doesn’t
produce very many eggs, then this multiple egg retrieval strategy might be a good choice
for you.
Did you know that many IVF experts are no longer doing fresh embryo transfers at all?
Check out this playlist to learn more.
But before you go,