By Dr. Surveen Ghumman Sindhu: Before blastocyst culture started IVF embryos were transferred at day 2 or day 3. However in recent years blastocyst culture media was introduced and it made it possible to grow the embryos upto day 5 outside the body.
What is a blastocyst?
Usually a day 3 embryo consists of 8 cells which are all similar is size shape and components. A blastocyst will have further development into two different cell components – the trophoectoderm and the inner cell mass. One forms the placenta and the other the fetus. There is a central fluid filled cavity called blastocele. The blastocyst is graded according to quality of trophoectodem and inner cell mass, appearance of blastocele and expansion of the cell. Blastocyst one expanded may hatch any time from day 5 to 7.
Why blastocyst culture was not done earlier?
After day 3 the embryo requires a different culture environment. Certain media with specific nutrients for blastocyst growth were developed. It is the introduction of this media which made the growth of embryos possible outside the body.
Advantages of blastocyst or Day 5 culture.
1. Many times day 2 or 3 embryo do not grow into good quality blastocysts which may yield a pregnancy. However there is no test by which we can identify these embryos. Blastocyst Transfer ( Day 5) allows better selection of embryos ie only those embryos which are good can grow to blastocyst stage. This allows us to choose the most competent ones.
2. Better embryo quality yields higher implantation and pregnancy rates
3. It reduces chances of multiple pregnancy as only one or two need to be transferred
4. Day 2/3 embryos are normally found in fallopian tubes. They reach uterus by day 5 when they are ready for implantation. Blastocysts are put in the uterus at the time when the lining of the uterus is most receptive like in a natural cycle. Transfer is done just before implantation and invasion of embryo in uterine wall.
1. Blastocyst culture is dependent on the culture conditions and lab environment. If these are not good blastocysts will not develop
2. On day 3 patient may still have a chance of pregnancy with good grade embryos after transfer but if embryos do not grow they have no chance at all as there is no embryo transfer.
Blastocyst formation rate:
This is the percentage of embryos which form blastocyst. It ranges from 25-65% and depends on
1. Quality of embryo
2. Quality of culture conditions and lab environment.
Do blastocyst cultures and transfer give higher pregnancy rate ?
Most studies show an improved pregnancy rate. Some centres show no change in rate. Some laboratories are unable to maintain stable conditions leading to poor blastocyst development. The pregnancy rate is variable in different labs.
Criterion for going in for blastocyst culture:
The criterion which is taken for blastocyst culture is that there should be at least 4 or more day 3 embryos of good quality. If there are less than 4 embryos blastocyst culture is not recommended.
Blastocyst transfer is an advanced technique with several advantages and centres doing it are confident of excellence in their lab and culture conditions.