BLASTOCYST CULTURE AND TRANSFER

Embryo transfer on day 3 (cleavage stage) is performed three days after fertilization when the embryo is at an earlier stage with fewer cells, while blastocyst transfer occurs on day 5 or 6 when the embryo is more developed. In the human body, the embryo doesn't naturally implant at day 3 but after reaching the blastocyst stage. In traditional day 3 transfers, two or three embryos may be transferred to increase implantation chances, whereas only one blastocyst is typically transferred because a natural selection process has already occurred, with only the strongest embryos surviving to this stage. Research shows that transferring fresh embryos at the blastocyst stage may lead to more live births than cleavage-stage transfers, with success rates increasing from 31% to between 32% and 41%.

Blastocyst culture allows for the selection of more developed embryos, which significantly increases the chances of successful implantation. There are two central advantages: firstly, it is physiologically more appropriate, as embryos naturally reach the uterus at the morula stage (day 4) or later in vivo, and exposing early-stage embryos to the uterine environment prematurely may cause stress and reduce implantation potential. Secondly, blastocysts have higher implantation potential because only the most viable embryos develop to this stage through self-selection. While morphological criteria for selecting day 2-3 embryos are limited, and studies show that 80-90% of morphologically-normal day 3 embryos fail to implant, blastocyst transfer reduces chromosomal abnormalities from 59% in day 3 embryos to 35% in day 5 blastocysts for women over 36.

No, not all embryos develop into blastocysts; only the best quality embryos are able to reach this stage. Some embryos may not grow to the blastocyst stage, which can reduce the number of embryos available for transfer. In some cases, if no embryo develops into a blastocyst, the cycle may need to be canceled. This natural selection process, while sometimes resulting in fewer embryos available, ensures that only the strongest and most viable embryos are identified for transfer. For women with fewer eggs or embryos, early embryo transfer might sometimes be a better option.

Blastocyst transfer offers several significant advantages: higher success rates with better chances of implantation due to more developed embryos; better embryo selection as only the strongest embryos survive to the blastocyst stage; fewer embryos needed for transfer, which helps lower the risk of multiple pregnancies while maintaining good success rates; closer alignment to natural timing, matching the natural process of when an embryo enters the uterus; and improved outcomes after previous failures, particularly beneficial for patients who had no success with day 3 transfers. Additionally, blastocyst transfer results in increased pregnancy success rates and better synchronization with the uterine environment.

While blastocyst transfer is highly beneficial, it has some limitations and risks. The primary concern is that some embryos may not survive to the blastocyst stage, reducing the number of available embryos for transfer. Blastocyst culture requires advanced laboratory conditions, highly controlled environments, and experienced specialists to maintain optimal growth conditions. Waiting the extra days to see if embryos survive can increase emotional stress for patients. For women with fewer eggs or embryos, early embryo transfer might be more appropriate. The extended culture period means embryos spend more time in an artificial environment, though modern laboratories use advanced incubators and time-lapse monitoring to optimize conditions.