1. Blastocyst culture and day 5 embryo transfer for in vitro fertilization allows selection of the best quality embryos for transfer.
2. Embryo's quality is important with infertility
3. With blastocyst transfer, we transfer fewer embryos – reducing multiple pregnancy risks, and maintain high IVF success rates.

Definition of a blastocyst

1. An embryo that has developed for five to seven days after fertilization and has 2 distinct cell types and a central cavity filled with fluid (blastocoel cavity).
2. The cells in a blastocyst have just started to differentiate.
3. The surface cells that surround the cavity (just under the outer shell) are called the trophectoderm and will later develop into the placenta.
4. A more centrally located group of cells – the inner cell mass, will become the fetus.

Blastocyst development

The most commonly used indications for assisted hatching with an in vitro fertilization case are:

1. The blastocyst usually forms on day 5 as fluid builds within the compacted morula.
2. A healthy blastocyst often begins hatching from its outer shell, called the zona pellucida between day 5 to day 7 after fertilization.
3. Within 24 hours after hatching, embryo implantation after IVF (or a “natural” pregnancy) begins as the embryo invades into the uterine lining.
4. The blastocyst releases HCG hormone (the pregnancy test hormone) which leaks into the mother’s blood as the embryo implants.

Blastocyst formation rate

The goal of in vitro fertilization and embryo culture is to provide high-quality embryos which are capable of continued development and result in live births. However, under standard IVF culture conditions, only about 25 to 60% of human embryos progress to the blastocyst stage after 5 days of culture.
The low rate of embryo development has 2 main causes:

1. A less than optimal culture environment in the lab dish.
2. The inherent “weakness” of human embryos.

Advantages of blastocyst transfer for IVF

1. 2 to 3-day-old embryos are normally in the fallopian tubes, not in the uterus. The embryo gets to the uterus about 80 hours after ovulation.
2. The embryo implantation process begins about 3 days later – after blastocyst formation and hatching out of the embryonic shell have occurred.
3. In vitro culture conditions are maximized so healthy blastocysts form at a high rate, then day 5 blastocyst embryo transfer is done.
4. The uterine lining on day 5 should be receptive to the arriving embryo – this is a more “natural” time for the embryos to be in the uterus. It is the same timing as with a natural pregnancy.
5. The transfer is done shortly before the time for actual invasion and implantation.

Pregnancy rates and reducing the risks for multiples

1. Transferring blastocysts following IVF also provides another potential benefit – reducing the possibility of multiple pregnancies.
2. Many 2 or 3-day-old embryos do not have the capacity to become high-quality blastocysts and make a viable pregnancy. However, on day two or three of culture we don’t have methods to determine which embryos will be viable long-term, and which will soon arrest their development.
3. We can then transfer fewer embryos and still obtain high pregnancy success rates – with very little risk for having high order (triplets or higher) multiple pregnancies.