The advantage of a day 5 blastocyst transfer has to do with selection. These days most reputable programs are putting 2 embryos back in youngish women (I know what you’re thinking, but we’ll skip the octo discussion). Anyway, let’s say you’re lucky and have 5 nice embryos on day 3. Even though some may look a litter nicer than others, we really may not be able to tell which embryos are the best ones. So, we can wait 2 more days. In that time, some embryos may not grow well, but probably those embryos would not have survived in the uterus anyway.
The advantage here is that the embryos that do survive are probably stronger, and these can give you a better chance of pregnancy. It’s like a stress test, those that pass are probably better. One of my partners puts it nicely: just because a horse is leading ½ way around the track doesn’t mean it’s going to win the race.
But not all programs use the day 5 transfers, and some do it selectively i.e. only in some patients. Why is that? Some of it has to do with initial experience. At NYU, our initial experience was excellent, in fact better than expected, so we felt very comfortable continuing with it and this led to more and more cases and more expertise with time. Other programs had a bad experience initially. They were therefore less eager to increase their blast cases. Once something does not go well, especially in medicine, it’s really hard to go back to it.
Why would there be different experiences in different programs? Hard to say. I am prejudice in favor of the NYU lab, the people are all excellent, but there are other good labs around.
It may have something to do with the media. Media is the nutrient juice we grow your embryos in. We used to make it from scratch (what a pain), but now we buy it. An important factor making blast possible is the media. The old types of media could only support an embryo in culture for 3 days, and some very important changes in media composition were necessary to allow the embryos to grow 2 more days in the lab.
Initially, there was some variation in the new blastocyst media composition and quality, and there were batches that did not grow blastoctys well. So if you were an IVF lab who just happened to start out with an inadequate media batch, your outcomes would be lower, and you would be reluctant to explore blast culture further. Thanks to your lab directors and staff, we had a very careful process of testing media and analyzing which worked best. This allowed up to keep up the embryos quality in the face of variable conditions.
Among the programs that go to day 5, there is considerable variation in their criteria for going to blast. Some IVF centers need you to have 10 nice embryos on day 3 before they will consider growing the embryos longer. Others need you to have 6 day 3s, some 5, etc etc. Programs also put age in the mix; in other words less likely to go to day 5 the older you are. The more comfortable a program is with blastocyst, the softer their criteria will be.
Our criterion is that if you have more embryos than we want to transfer, you go to day 5. We transfer 2 embryos in most women which means if you only have 2 viable embryos on day 3 we do the day 3 transfer. If you have 3 or more, as is usually the case, you go to day 5.
Naturally, the obvious by-product of a good blast program is a lower multiple rate. Getting you better selected embryos, will help you become pregnant with fewer embryos. We started with blastocyst transfer in 1999. At the time we had a 20% of women under 38 had 3 embryos implant and now the rate is 1.9%. And many of those women had 2 embryos transferred, but had one of them split into identical s.
We went from putting in an average of 3 embryos per patient to two. Our pregnant rates would not be as high as they are if we put 2 embryos in on day 3. It’s just too hard to tell which are the best ones on day 3. Besides we have numbers to support our work. The implantation rate per embryo (this is a number that is used a lot. It’s the odds of each embryo sticking) was 34.5% in women under 35 and now its 43.4%.
So if your program is not doing a lot of blastocyst, does this hurt your chances? It really depends on the published pregnancy rates from your clinic. If they have great rates, but don’t do much blastocyst, that’s not so bad. Unless of course they are putting in more embryos per transfer to maintain the higher pregnancy rates. It’s not always easy to predict who will not get pregnant and who will get pregnant with triplets or quads. If you want to avoid 3s and 4s, your best bet is to not take the risk.
Sometimes there can be a diagnostic advantage to blastocyst transfer. If you are not getting pregnant with day 3 transfers, it may be time to try blastocyst. Occasionally, the embryos look much worse on day 5 than they did on day 3. This would not be not good news but at least you would know where you stand. It is also possible that they look just ok on day 3, but perk up very nicely by day 5, and this information might be of help to you.
Thanks for reading, and please see disclaimer 5/17/06.