Culturing embryos in the laboratory

Our experienced scientific team, who oversee the laboratory fertilisation of the collected eggs and nurture the growing embryos before they are transferred back into the uterus, are a critical part of the success of Genea Hollywood Fertility. 

The science behind Genea Hollywood Fertility

In vitro fertilization (IVF)

At the time of egg collection, our scientists are looking for mature eggs with smooth borders and a fluffy corona of cumulus cells encircling them. Immature eggs, or those that have gone past optimum maturity (postmature), have irregular borders and poorer quality cumulus.

In conventional in vitro fertilisation (IVF), about 50,000 to 100,000 washed sperm are left in a small dish with the mature eggs. The sperm spend the next few hours attempting to penetrate the corona of cumulus cells. Hopefully one sperm will be successful and fertilise the egg.


In Vitro Fertilization


Intracytoplasmic sperm injection (ICSI)

A special technique called intracytoplasmic sperm injection (ICSI) can be used to fertilise eggs when there is thought to be a limited opportunity of fertilisation occurring with conventional IVF. This might be either because of problems with low sperm numbers or low sperm motility, or because of other barriers to the fertilisation process such as sperm antibodies or previous failure to fertilise through IVF.

During ICSI, a single sperm is injected into each egg. The sperm is selected mainly on the basis of its normal shape and size.

Blastocyst culture

Once fertilisation has occurred the embryo will divide and rapidly increase in cell numbers over the next few days.

By Day 4, the cells have divided rapidly but the embryo has not yet increased in size. It is now ‘compacting’ (you can’t distinguish the cells) and is called amorula.

If the embryo survives to Day 5 – the blastocyst stage – it will contain between 75 and 100 cells. It is a 3-dimensional ball of outer cells (the trophectoderm) surrounding a fluid-filled cyst in which an inner group of cells (the inner cell mass) can be seen.


Blastocyst Culture


The trophectoderm will go on to form the placenta, membranes and umbilical cord, while the inner cell mass will become the baby.

It is not possible to tell the difference between a ‘good’ embryo and a ‘bad’ embryo just by looking at them. Embryos at the best of times are busy transforming and repairing themselves, so can develop fragmentation (when small bits of cells are pinched off during division) or vacuoles (which are small spaces within the substance of the cells). The significance of these changes is not known and many fragmented and vacuolated embryos can go on to form perfectly healthy pregnancies.

While many embryos can survive 2 or 3 days to reach the 4-8 cell stage, only the strongest will have the ability to keep developing into a blastocyst and then a baby. One way of identifying the better embryos, therefore, is to let them grow a little longer in the laboratory and to transfer them at the blastocyst stage. This is a good way of determining which embryos have the most developmental potential and maximising the potential of a successful pregnancy.

Our great success with blastocyst culture and implantation means that blastocyst transfer is a standard part of our service at Genea Hollywood Fertility.


An embryo’s energy supply comes from tiny structures inside its cells called mitochondria. Until it has implanted and formed a placenta, the embryo relies on the energy produced by the mitochondria it has inherited from its egg. Because females are born with all the eggs for their lifetime, the egg mitochondria are essentially the same age as the woman herself.


Embryos must also have the right genetic makeup to develop normally. In humans, genes are contained in 23 pairs of chromosomes. An incorrect number of chromosomes leads to failure of an embryo to implant or to progress to a healthy baby. Pregnancy is a great filter of abnormal embryos. When chromosome analysis is performed on cells from Day 3 embryos, studies have shown that only one third will have the normal number. If an embryo progresses to Day 5 and becomes a blastocyst, it has a two-thirds chance of being chromosomally normal. 90% of chromosomally abnormal pregnancies will miscarry in the first trimester (first 12 weeks of pregnancy). 93% of chromosomally normal pregnancies will continue to term.


Proportion Of Chromosomally Normal Embryos


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