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What Can Blastocyst Do For You?

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.

Dr. Licciardi


  • Grifo JA, Flisser E, Adler A, McCaffrey C, Krey LC, Licciardi F, Noyes N, Kump LM, Berkeley AS. Programmatic implementation of blastocyst transfer in a university-based in vitro fertilization clinic: maximizing pregnancy rates and minimizing triplet rates. Fertil Steril. 2007 Aug; 88(2):294-300.
  • Gardner DK, Schoolcraft WB, Wagley L, Schlenker T, Stevens J, Hesla J. A prospective randomized trial of blastocyst culture and transfer in in-vitro fertilization. Hum Reprod 1998; 13(12):3434-40.
  • Quinn P. The development and impact of culture media for assisted reproductive technologies. Fert Steril 2004; 81(1): 27-29.

Meet the Blastocyst

Hello everyone, this blog will describe the blastocyst. I will show you some pictures and tell you what is good and what is less good. Next time I will tell you a little about our blastocyst experience at NYU.
Let’s start with an easy one, a nice one. This is a very nice blasotocyst.

This is the type of embryo you may see on doctor’s web sites.

So what are we looking for? In no particular order, one is the thickness of the zona. This is the thin membrane around the embryo; it looks like a clear plastic shell. The thinner the better. As the embryo grows, gets larger, and becomes ready to pop out of the zona. The zona gets thinner, and this is a good sign. We don’t measure the thickness; we just look at it and make a judgment. The bigger embryo in the picture below has a really thin zona, almost impossible to see, which is a good thing.

This embryo has a much thicker zona, not as good.

What else are we looking for? We look inside the embryo. You may not be able to tell by looking right away, but the inside is hollow. Thus the name blastocyst: the inside is like a fluid filled cyst. That’s a good thing. So the next embryos have a lot of space on the inside, the cavity (the space inside) is large, another good thing.

This familiar embryo has a smaller cavity, not as good, but not a terrible embryo overall.

What about the cells of the embryo? There are 2 types. There is the inner cell mass and the trophectoderm. The inner cell mass goes on to become the fetus/baby, the trophectoderm cells go on to become the placenta. Many more cells are designated for the placenta than are for the fetus. Ideally, the inner cell mass (ICM) is easy to see as a clump of tightly bound cells more towards the center of the embryo. Here is the nice embryo we saw before with a nub of cells at about 8 o’clock. This is a good-very good inner cell mass.

These embryos have ICMs that are smaller; in fact it’s hard to see the ICM in the bigger embryo.

Next we move on to the other cells of the blastocyst, the cells that make up the outer area. These are the trophectoderm cells, troph cells for short (really sorry about all the terminology, it just goes with the territory). Cells that are more plentiful and smaller make a better embryo. The larger embryo below has very nice troph cells (and the ICM is really nice too).

This embryo has troph cells that are not quite as good: they are larger and fewer in number.

The embryo on the left below has just a few troph cells and they are really spread out, not so good.

The next embryos are not very good looking. The top left does have a cavity, and the cells are not very good. The top right has a very small cavity. The bottom embryo looks like there is no cavity.

The next embryos have cavities, but not the nice ICM cells and troph cells we have previously seen.

These embryos have thick zonas, the lower left has no cavity, and the upper right has a small cavity and few large cells inside.

This poor embryo has a nice thin zona, but just a few cells inside. The troph cell at 4:00 o’clock is just spread so thin, across almost half the embryo. The ICM at 11 o’clock is tiny.

So now you know more about blastocysts than the average person undergoing infertility. I realize that some of you are not as interested in the details, and others really use the details to get through the infertility day.
Next time I will talk a little about the numbers we assign and a little about the NYU blastocyst experience.Thanks and see you sooner next time,

Dr. Licciardi


  • Prados F, Debrock S, Lemmen J, Agerholm I. The cleavage stage embryo. Human Reproduction, Vol.27, No.S1 pp. i50–i71, 2012.
  • Blake DA, Farquhar CM, Johnson N, Proctor M. Cleavage stage versus blastocyst stage embryo transfer in assisted conception. Cochrane Database Syst Rev. 2007 Oct 17 ;(4):CD002118.
  • Puissant F, Van Rysselberge M, Barlow P, Deweze J, Leroy F. Embryo scoring as a prognostic tool in IVF treatment. Hum Reprod 1987; 2(8):705-8.
  • Racowsky C. Combelles CM. Nureddin A. Pan Y. Finn A. Miles L. Gale S. O’Leary T. Jackson KV. Day 3 and day 5 morphological predictors of embryo viability. Reprod Biomed Online 2003; 6(3):323-31.