The very first IVF baby was born in 1978 in England. Not that long ago, if you think about it. The use of assisted reproductive technology has blown up ever since, and thousands of IVF babies are born each year. ha
Medical technology has improved tremendously throughout the past few decades. In 1990, preimplantation genetic diagnosis (PGD) was introduced, which helped parents screen for sex-linked diseases. And ICSI didn’t even exist before 1991! And way back in 1980, one of the first scientific studies reported a whopping 6% success rate per initiated cycle!
Surely, all the advancements in medicine have led to ever-increasing IVF success rates?
IVF Success Rates According to the CDC
Here in the US, we have the CDC. And other than failing at figuring out a cure for zombie-ism (Walking Dead – S1, when it was still cool), they also keep track of IVF success rates for pretty much all infertility clinics in the country. Every year, they publish the “ART Fertility Clinic Success Rates Report” and the “ART National Summary Report”. These reports are available on the CDC website dating all the way back to 2005 and is a treasure trove of data.
So. Much. Information!
We already looked at the IVF success rates in general in this post, but that doesn’t tell us how it compares to previous years.
I figured I might as well dive into these reports and figure out whether success rates have improved in the last decade (from 2005 to the most recent report from 2015).
So let’s dig right in and examine pregnancy and live birth rates per initiated fresh IVF cycle.
Pregnancy and birth rates per cycle, from 2005 to 2015
Looking at the table above, we see that success rates have remained remarkably steady from 2005 to 2015. Actually, that’s being generous. In the last 2 years, success rates have dropped to levels below of what they were 10 years ago! The rates seem best from about 2006 to somewhere around 2013. So why is that?
Mystery (partially) solved?
One possible, and in my view likely, contributor to this strange phenomenon lies in the number of embryos transferred per cycle. Back in the day, it was common practice to transfer quite a few embryos each go-around.
Improvements in cryopreservation techniques (from slow freeze to vitrification) made it possible to freeze and successfully thaw leftover embryos, without too much risk. Clinics began shifting to transferring just a single embryo among those with a good prognosis.
If you’re lucky enough to have several good embryos, then those embryos not used can be cryopreserved and transferred at a later date without having to go through a full IVF cycle again. This is what we call a frozen embryo transfer (FET). The good news is that pregnancy and delivery rates transferring one by one are similar compared to transferring multiple embryos at once.
The US has been somewhat slower to implement this than some European countries, but even in the US, it finally looks like transferring more than 2 embryos is losing popularity. More on that in a little bit. Let’s first take a look at the mean number of embryos transferred by year.
Back in 2005, the average number of embryos transferred was 2.65. I’m guessing that numbers were even higher before that.
Since 2005, there has been a steady reduction in the number of embryos transferred. In 2015 the number finally dipped below 2.
Since looking at charts is always nicer than tables, here’s the same data again in chart form:
Again, the number of embryos transferred shows a steady drop from 2005 to 2015. The pregnancy and live birth rates per cycle have been decreasing a little bit in the last few years too.
If multiple embryo transfers result in higher success rates, why would we even want to strive to decrease the number of embryos transferred?
Well, for starters, look at this chart from the 2015 CDC ART report:
1 in 3 mothers who had 2 embryos transferred had twins. Transferring multiple embryos greatly increases the odds of twins, triplets or even more (makes sense, right?).
Take a look at the success rates per transfer. The success rates per transfer are always higher than success rates per IVF cycle started. This is because cycles often get canceled either before egg retrieval or before transfer in case none of the embryos made it to transfer day. Out of the 91,090 cycles started, only 59,336 made it to transfer.
So the success rates (per transfer) are 36.2% among those who had a single embryo transferred, compared to 40.8% in those who had 2 embryos transferred. The success rates quickly drop when transferring >2 though, which probably has something to do with the patient demographics at that point (worse prognosis patients).
Back to the question. Why do we want to decrease the number of embryos transferred?
As you probably know, being pregnant and delivering multiples, result in greater physical stress for both the mother and infants. The chance of delivering a baby preterm and/or with low birth weight is around 5 times higher in twins than singletons, and is pretty much a given with triplets. The figure below looks at just that.
The Popularity of Single Embryo Transfers
While we saw that the mean number of embryos transferred dropped in the past decade, let’s have a look at exactly what caused this drop in average embryos transferred.
Over 10 years there was no real difference in the percentage of two embryo transfers. It’s actually gaining a little bit of popularity (8% over 10 years)! But, three and four embryos per transfer saw a huge drop, and the percentage of single embryo transfers saw a meteoric rise from 10.7% to about 33.5 percent.
The Final Blow
On top of all that, I can think of at least one other reason for the “lower” success rates in recent years. This may be speculative, but what seems to be happening is that in recent years doctors are more often choosing to transfer embryos as blastocysts (day 5). In the past (some clinics still do this), embryos were transferred at 3 days old. The so-called cleavage stage.
While scientific studies have shown that the pregnancy and live birth rates are higher with day 5 transfers, there is an increased chance of there not being an embryo left to transfer when waiting the full 5 days. This, in turn, increases the number of cycles where there is no embryo to transfer (so an automatic failure)! On the plus side, if your embryo(s) do make it to day 5, they sure are strong little survivors! It’s the best natural selection method currently available.
So is IVF Getting Better or Not?
Yes and no!
Let’s try to sum it all up:
- Pregnancy rates have been fairly stable in the past decade.
- Live birth rates have been fairly stable in the past decade.
- Day 5 transfers are becoming more common than 3-day transfers, potentially increasing the number of “failed cycles”, but also leading to an increased chance of implantation when a transfer does occur.
- More and more people choose to transfer a single embryo.
- When transferring more than 1 embryo the birth of multiples is common.
- There are risks associated with multiples, so if it can be avoided, it should.
- Single embryo transfers reduce the pregnancy rates slightly, but;
- Additional transfers of previously frozen embryos collected from the same stimulation cycle result in similar pregnancy rates.
Are IVF doctors getting better? Probably. The fact that the rate of >2 embryos transferred per cycle are decreasing (leading to fewer infants that are born prematurely or underweight) tells us that we’re heading in the right direction. Doctors no longer need to increase their success rates by transferring as many embryos as possible. They have better alternatives. That, to me, tells me that IVF is indeed getting better.
Edit by Mrs. Frugalcrib: So our Instagram followers posted a lot of interesting theories on why we see that slight dip in success rates over the years. Most said they expected an increase in age to contribute to what we’re seeing. I decided to check it out.
While the CDC doesn’t give us exact age details, they do mention the mean age of all women who underwent IVF. Since 2005, the mean age has been 36 every single year. Those younger than 35 still make up the largest proportion of women undergoing treatment, that hasn’t changed either.
So while it’s certainly an interesting idea, I don’t think age can fully explain the (slight) decline in success rates per initiated cycle. Just like with many things in life (and science!) there’s rarely a single reason for any occurrences.