IVF Babble

Embryos, blastocysts and hatching – what does it mean?

The terminology that comes with a fertility diagnosis and IVF can cause concern for many, so we wanted to take the ‘terms’ out of the ‘ology’ by asking CARE Fertility to explain just some of the words you will come across…

What is the difference between an embryo and a blastocyst?

A blastocyst is the term given to an embryo when it reaches a particular developmental form with a fluid filled cavity, a mass of cells (destined to become the foetus) and other surrounding cells (destined to become placenta).

When does an embryo turn into a blastocyst?

An embryo, about four to five days after fertilisation reaches the blastocyst stage.

Does it always turn into a blastocyst? If not, can you still do a transfer?

Sometimes embryos do not develop into blastocysts. Some clinics may transfer them, depending on their stage and quality but if it is clear that they have stopped developing earlier, they are not transferred.

Can you explain hatching? Does this always happen to a blastocyst?

Hatching is the term used when the blastocyst cells start to break through the shell (zona pellucida) of the embryo. Hatching may not always take place but it is a necessary step towards implantation and pregnancy.

Can you explain assisted hatching? Do you always assist if hatching doesn’t happen naturally?

Assisted hatching is used in some clinics to make a small hole in, or to thin, the shell of the embryo in an attempt to help it hatch. There are arguments for and against this practice. However, most blastocysts are transferred to the womb before they start to hatch with the aim that this will occur naturally.

Why do some perfect embryos that turn into a blastocyst then hatch, just not work?

There are many reasons why apparently perfect looking embryos do not result in pregnancy. It may be due to difficulty hatching (but this is not considered a major reason), to chromosomal irregularities or to the conditions being suboptimal in the womb, for example.

This video of a time lapse incubator captures the amazing early stages of a blastocyst happening

Embryo becoming a blastocyst

What is a mosaic embryo?

PGS testing explained




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