The first 5 days of an Embryo

This guide will help you understand why we culture embryos up to Day 5 and why we transfer on either Day 3 or Day 5.

Day 0

Once an egg is collected, it is washed and prepared for either insemination (IVF) or ICSI. Sperm is similarly washed and primed for the chosen procedure. Following whichever treatment was opted for, the egg is incubated in conditions tailored to support development.

Day 1

The morning after fertilisation, the egg is checked to confirm that fertilisation has occurred. Assuming fertilisation is successful, the embryo enters the early stages of development and needs to be carefully cultured to monitor its progress.

Our EmbryoScope incubator is ideal for this stage, as it provides continuous, uninterrupted culture while photographing the embryo every ten minutes. This creates a detailed time-lapse video that helps embryologists closely observe the embryo development day by day during the IVF embryo stages.

By tracking the embryo’s growth at each step, we can better understand its health and readiness, particularly as it approaches the crucial day 5 embryo stage, when it typically reaches the blastocyst phase.

Day 2

By this stage, the embryo’s single cell should have replicated into two cells, and those may have further divided to form a four-cell embryo. The EmbryoScope’s ability to capture continuous images overnight is instrumental in helping embryologists track embryo development day by day during IVF.

This detailed view allows specialists to assess whether the cells have divided normally and to identify any signs of abnormal development early in the IVF embryo stages.

Day 3

The cells will keep splitting into two in a healthy embryo, gradually increasing the cell number. At this point, it may be decided to transfer the embryo back into the uterus. This is because despite huge developments in science and the ability to sustain embryos in the lab, the uterus is still superior and naturally gives them the best environment to grow in.

However, if there are several embryos from the same couple, many of them may look similar at this stage, making the clinical decision as to which should be transferred quite difficult. In order to see which of several are the healthiest, they can remain in the incubator a further two days. Those which survive this have proven themselves to be extremely good candidates for transfer and a successful pregnancy.

Day 4

On day 4 of embryo development, the embryo’s cells begin to compact as they prepare to form a blastocyst. At this stage in the embryo development day by day IVF process, embryologists do not grade the embryo because compacting embryos tend to look quite similar, providing little indication of their overall quality.

Day 5

By day 5 embryo development, a healthy embryo will have formed a blastocyst, dividing its cells into sections that will develop into the foetal matter and placenta. At this stage in the IVF embryo stages, the blastocyst is graded from ‘A’ to ‘D’ based on how well these parts have formed. Unless graded as ‘D’, the embryo can be transferred into the uterus. During the embryo transfer, the blastocyst is placed in a catheter, which is carefully inserted through the cervix and positioned by a clinician in the optimal location within the uterus.

Spare embryos of a high enough quality are ideal for freezing, and may be used in the future for further attempts or siblings.

After Day 5

On its sixth day, the embryo should be hatching out of its protective membrane, in order to begin implanting into the uterine lining.

Slightly slower embryos may only reach their full potential as a blastocyst on day 6. These can-and regularly are- be frozen on their sixth day, and kept as a reserve.

For Further Information

If you would like any further information then why not come to one of our patient information evenings where we explain in detail the whole IVF process. Alternatively, you can call and arrange an informal chat which is an ideal opportunity to come and meet the team, see the facilities and most importantly where we can get to know you