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Blastocyst, blastocyst, blastocyst

Date : 10-01-2014
Tags: Blastocyst 

Blastocyst, blastocyst, blastocyst!

What is a blastocyst?

A blastocyst is the stage the embryo reaches after 5 days in culture from the egg retrieval. During the three first days of development the embryos start to divide in separate cells and they are called cleavage embryos. It is only from day 3 to day 5 that the blastocyst is formed. The blastocyst is a much more complex structure than that of the cleavage embryo. The number of cells has increased to reach over a 100. Under the microscope it is even possible to distinguish the two different cell types that have started to develop. The first of these cell types is known as the Inner Cell Mass (ICM), this is earliest sign of fetal development and is the part of the blastocyst that develops into the baby. The second of the cell types is known as the trophectoderm or trophoblast. These are specialised cells which develop the placenta and are important in embryo implantation.


Why are blastocysts important?

While the majority of fertilised eggs will develop into a three-day old embryo, only perhaps 40% of these embryos will develop into a blastocyst. Therefore, blastocysts are considered to be a more "select" group of embryos with a higher chance of pregnancy.

What is the advantage of blastocyst culture?

Sometimes it is not possible to select the best quality embryo(s) to transfer and the day 3 stage. This is because at this stage all the embryos can still look relatively similar and it is impossible to select which embryo is capable of forming a pregnancy over those which are unlikely to. In such circumstances there is a tremendous advantage to let the embryos develop on for another 48 hours and allow them to develop into blastocysts.

Subsequently by letting the embryos develop to the blastocyst stage the embryologist will be able to make a better choice of which embryo(s) to transfer back. We achieve higher pregnancy success in doing this because those embryos that manage to become blastocyst in the lab have a higher potential to implant in the womb. Accordingly, we advise that if embryos develop into good quality blastocysts we replace a fewer number. This is because a blastocysts has a much greater potential to form a pregnancy and therefore it is more likely that a multiple pregnancy will develop if we transfer more than one.

What is the difference between a normal embryo transfer and a blastocyst transfer?

The transfer procedure for a blastocyst is identical to that for a normal embryo transfer. However, the key difference is that a blastocyst is implanted back into the womb five to six days following the egg collection whereas an embryo is implanted two to three days following egg collection.

What are the risks of a blastocyst transfer?

Not every embryo is capable of forming a blastocyst. Therefore, there is the small possibility that the IVF cycle may not result in a transfer of any embryos if none of the three-day old embryos develop into blastocysts. We believe that if blastocysts development does not occur, it is unlikely that a pregnancy would not have developed if the embryos had been transferred at the 3-day old stage.

In practice however, it is very rare for no embryos to develop to a blastocyst. If the embryologists have any concerns about the development they will discuss the possibility of transferring the embryos back into the womb earlier and not letting them develop to blastocysts.

What are the results from blastocyst transfers?

In the table below there are the results of the pregnancy rates at CRM CARE London after blastocyst transfer. 1st Jan 2012 to 31st Dec 2012 (for fresh IVF & ICSI cycles): 

Patient Age < 35 35-37 38-39 40-42 > 43
Pregnancy Rate 64.3% 62.2% 65.0% 52.6% 26.7%
Clinical Pregnancy* 51.2% 51.4% 42.5% 34.2% 20.0%

 * Clinical pregnancy signifies the presence of a heartbeat on scan, per blastocyst transfer

 If there are any questions you have from reading this blog please contact CARE Fertility

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1978 - World's first IVF baby

1981 - First male factor patient treated

1982 - World's first baby delivered after intrauterine sperm/egg transfer

1984 - World's first baby from blastocyst transfer

1990 - World's first baby born after micro-injection

1992 - Britain's first SUZI treatment baby

1992 - Britain's first "sugar drop" frozen embryo baby

1996 - World's first testicular spermatid baby

2007 - Europe's first baby born following embryo screening using Comparative Genomic Hybridisation (CGH)

2009 - Birth of World's First baby following array CGH screening

2010 - UK's first baby born through PGD for HLA tissue matching

2010 - Blastocyst Chromosome Screening - UK's first baby born

2010 - First multi-factorial genetic chromosome tissue typing and translocation analysis of embryos in an IVF cycle

2010 - First UK based total treatment cycle for PGD and HLA Tissue Matching - Fanconi Anaemia

2011 - First UK pregnancy following use of an Embryoscope

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