I have been getting some interesting questions lately about IVF pregnancy rates such as “I’ve
heard that people never get pregnant on the first try, is that true?” or “Is the success rate for
IVF higher on the second try” “Does the uterus need a few ‘practice runs’ before a pregnancy can
happen?” Today, on InfertilityTV, I will discuss what the science says about these questions.
In order to have a discussion about pregnancy rates, we must first make sure that we are
all talking about the same concepts. Let’s say 100 couples have gone through an egg retrieval
and each couple has three embryos frozen. Those 100 couples then start their frozen embryo
transfer preparation. A single embryo is thawed and transferred for each couple. For this example,
we will assume that 100% of the embryos survive the thawing process. This isn’t always the case,
however. During the first embryo transfer attempt, sixty couples become pregnant. That is a pregnancy
rate of 60%. This leaves 40 couples who did not become pregnant. Those 40 couples then
go through a second embryo transfer and 24 of the couples become pregnant. For this second attempt,
the pregnancy rate is again 60%. No difference. The pregnancy rate in the first and second attempt
was the same. IVF doctors will say that the pregnancy PER TRANSFER is the same. However,
you can also calculate the total number of couples who became pregnant over both attempts. Sixty
couples became pregnant on the 1st attempt and 24 couples became pregnant on the second attempt.
The total is 84. IVF doctors will say that the cumulative pregnancy rate over two attempts is
84%. This is a very important point. The pregnancy rate on each attempt was the same - 60% - but
the cumulative rate over two cycles was 84%. People commonly get this confused and mistakenly
believe that the pregnancy rate on the second attempt ONLY is 84% - but this is not correct.
With that background,
what do the numbers look like where I work at the Naperville Fertility Center.
So far this year, I have performed 300 frozen embryo transfers. 217 of those we
performed on patients doing their 1st, 2nd or 3rd attempt. Eight days after the embryo transfer, we
perform a blood test to look at their hCG level. A patient was diagnosed as pregnant if their hCG was
greater than 5 and then increased two to three days later. Since we know that
pregnancy rates decline in older women, we divided the patients into three groups.
Group 1 were transfers in which we used embryos that were tested for chromosome abnormalities.
This is known as PGT. The chance for pregnancy with tested embryos does not differ by age - one
we know the embryo is normal, older and younger patients have the same chance for pregnancy..
Groups two and three were transfers with untested embryos in younger and older women.
Here are the pregnancy rates for tested embryos. As you can see, the pregnancy rates were roughly
the same whether it was the first, second or third attempt. For younger patients with
untested embryos, again there was no difference in the chance for pregnancy through three attempts.
For older patients, the pregnancy rate was the same through two attempts
and decreased a bit on the third attempt.
So let’s go back to those questions that I have been getting. Question 1 was “I’ve
heard that people never get pregnant on the first try, is that true?” Clearly,
that is not true. Pregnancy rates on the first attempt were the same as with subsequent attempts.
Question two was “Is the success rate for IVF higher on the second try?”
We have now shown that this is not the case. Question three was “Does the uterus need a
few ‘practice runs’ before a pregnancy can happen?” Clearly, this is not true either.
Lets look at one more question. If couples do a second transfer, it is either because
their first attempt failed - meaning they didn’t get pregnant or miscarried on the first attempt
or they became pregnant and delivered and are now coming back for a second child.
These are two very different situations. It brings up another question: “Is the chance
for pregnancy better if the first attempt resulted in a delivery? Looking at our data, I was not able
to show that couples with a previously delivery had a better chance on their next embryo transfer
Our InfertilityTV Bottom line is this. The pregnancy rates with frozen embryo
transfers don't change much over three attempts. On average, your chances for
getting pregnant on your 1st try is similar to the chance on your second or third try.