Increasingly, the trend has been to transfer embryos at the 5-day blastocyst stage. I have discussed this with many clients and tended to agree with most consultants that 5 days is optimal for a number of reasons:
- The embryo has developed to a significant stage beyond 3 days when many embryos arrest.
- The environment in the uterus is consistent with the timing of a blastocyst emerging from the fallopian tube.
- Blastocysts are more mature and have a higher likelihood of being chromosomally normal.
However, research in the Netherlands has concluded that the chances of women giving birth after fertility treatment is about the same, regardless of whether their transfer was a Day 3 cleavage embryo or a Day 5 blastocyst.
In the study, 1202 women were randomly assigned to have either a day 3 or day 5 transfer, fresh or frozen. The overall findings showed no significant difference; 609 blastocysts were transferred, resulting in 58.9% live births compared to 58.4% from 3-day transfers.
However, there were some significant differences in the sub-groups. Women aged 36 years and above were more likely to be successful if blastocysts were transferred, with 52% live births compared to 43% for cleavage transfers. For those up to 36 years, the opposite was true, with 67% of 3-day transfers resulting in live birth, and 63% of blastocyst transfers. While this is not statistically significant, the researchers argue that it is clinically significant, and with an expanded sample size, the numbers would likely become statistically relevant.
The study also revealed that fresh embryo transfers tended to be more successful when blastocysts were transferred (37% vs. 29.5% for 3-day embryos). Meanwhile, Emma, the embryologist at Evewell, has stressed the importance of good technology. Timelapse incubation means you don’t need to disturb the embryo at any stage of development, but it is possible to easily check the progress of the embryo from the start. By reviewing the images taken during the time-lapse process, important information can be revealed.
For instance, a 3-day cleavage embryo will not survive to the blastocyst stage if, during the embryo cell’s first division, it divides into 3 cells instead of 2 cells. However, this crucial detail could easily be missed, as the embryo might still appear perfect on Day 3.