IVF experts have known for some time that the number one reason why older women have lower
IVF success rates is due to the increasing percentage of embryos with chromosomal
abnormalities. But are there other reasons? What if you only looked at the transfer of
tested embryos? Would you still see success rates decline with age or not? Stay tuned and find out
Let's start with some facts. Fact. The eggs you have in your ovaries today were produced before
you were born. Fact. Over time, the number of eggs declines and the quality of the eggs
gets worse. Fact. Because of this decline in egg quality, older women produce more
embryos with chromosomal abnormalities. The older you get, the worse it gets.
The most common type of chromosome abnormality is when an embryo has too
many chromosomes or too few. This is known as aneuploidy. Embryo testing during IVF is
called preimplantation genetic testing or PGT. When looking for abnormalities
in the number of chromosomes, it is called PGT for aneuploidy or just PGT-a for short
Now, if I did a single embryo transfer on ten 32 y/o women, on average, I would be transferring a
chromosomally abnormal embryo in four of them. If I did a single embryo transfer on ten 42 y/o
women, I would, on average, be transferring an abnormal embryo into 8 of them. The live
birth rate for a transfer of a single embryo in a 32 y/o that has not been tested is around
48%. The live birth rate for the 42 y/o with an untested embryo would be just over 10%.
However, a number of studies have shown that the live birth rate in older women who have
transfer of a single TESTED embryo, that is, an embryo without chromosome abnormalities,
is much higher than when an untested embryo is transferred. It seemed that once we removed
the embryos with chromosomal abnormalities, older women did just as well as younger women.
Recently, an analysis was conducted looking at the impact of age on live
birth rates. Because trends are easier to identify if you have larger numbers,
the analysis combined the results of several studies into one larger study. This is known
as a meta analysis. In total, they were able to look at close to 12,000 embryo transfers.
The researchers found that compared to women who were under the age of 35, those who were
over the age of 35 had about a 6% lower chance for live birth even though they transferred a
chromosomally normal embryo. In fact, the older the group they looked at, the lower the success
rate became. 42 year olds had about a 10% lower live birth rate compared to women under 35.
They also also looked at data from the U.S. IVF registry and found the numbers were very similar.
Can we determine at what point in the process, these chromosomally normal
embryos are failing? Yes. Looking at one of the large studies in this analysis,
we can see that most of that decline was due to failure of the embryo to implant
rather than an increase in the risk for miscarriage after implantation.
We still don’t know why these rates declined in older women but there are
a few possibilities. First, it could have something to do with the uterus.
Recent studies indicate that when embryos from young donors are transferred into older women,
pregnancy rates are very high but also decrease by about 10% when the recipient
age increases from 30 to 50 years old. Second, it is likely that there are other
kinds of abnormalities in the embryos that can get worse over time such as the accumulation
of genetic mutations or degeneration of some of the chemical processes that occur in the eggs.
Our InfertilityTV Bottom line is this. Chromosome abnormalities are the biggest part of the story
when it comes to the decline in fertility with age but there are other factors that can still affect
the chances for an older woman to have a live birth even when using chromosomally normal embryos