So what happens after day 3? Two days later we would like it to be a blastocyst. The day before it becomes a blastocyst, it should be a morula. A morula forms when the 8 cell embryo divides further, and at the same time the cells become very close to each other. Here it’s difficult to see the borders of the cells, so the morula looks like one big blob. It ‘s solid in the middle. It’s still inside the shell. There are about 12-30 cells in a morula. Here are some pictures:
Here is a nice looking morula.
Here are a few others . The top right looks nice, the others look OK, the bottom right looks the worst.
Most morulas (some write the pleural morulae, but most write it morulas) look about the same, so we don’t give them a number or a grade. We may say “nice” for a good one, but that’s about it.
Is it ok to transfer a morula? If your doctor wants to transfer your embryos on day 4, you will probably have morulas, but it will be hard for you to get a handle on quality. Most programs transfer day 3 or day 5. Day 4 transfer is ok, but most of us would say if you are waiting till day 4, just wait till day 5 so that the embryos have more time to grow, and quality can be better assessed.
What if on day 5 you are told the best embryos are morulas, not blastocysts? Not so good. I have had patients get back 2 morulas and become pregnant with twins. However the chances of pregnancy are much higher if you have blastocysts.
If there are morulas on day 5, isn’t it better to wait another day until they are blastocysts? No, because even if they become blasts on day 6 they are still a day behind. Rarely, we transfer on day 6. This may happen if , for example, there are 4 morulas and we want to give them, one more day to see which ones, if any, develop a little more.
Can we do anything to make the embryos grow faster? The same answer as last time. We try to change things up a bit next cycle, but there is no special drug protocol for slow embryos. Its just a matter of trying again and hoping for a better outcome.