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World DNA Day

On World DNA Day, Stephanie Gadd, Laboratory Director at CARE Fertility Bath, explains how DNA affects fertility treatment and how we analyse embryos’ DNA to identify the embryos which are chromosomally normal.


What is DNA?

DNA (deoxyribonucleic acid) is the chemical that all forms of life on earth use as “instructions” about how to develop and function. It’s present in virtually every cell in your body and contains the genetic code which is unique to you.

World DNA Day celebrates the date James Watson and Francis Crick published their research on the structure of the DNA molecule, on 25 April 1953. Their work paved the way for countless scientific discoveries which led to major advances in the diagnosis and treatment of diseases.

The shape of DNA was shown to be a “double helix”, rather like a long, twisted ladder in which the rungs hold the genetic information. DNA molecules are very long and are coiled up very tightly into chromosomes.


How is this relevant to IVF treatment?

Most cells in the body contain 46 chromosomes (23 pairs, one chromosome from each parent in each pair). Mature eggs or sperm contain half that number - 23 single chromosomes – which happens though a process called meiosis. Meiosis involves many steps where pairs of chromosomes duplicate, interact and then separate.


Analysing sperm at CARE Chester using Computer Assisted Sperm Analysis.


When a sperm fertilises an egg, the resulting embryo should have 23 pairs of chromosomes, one of each pair from the egg and the sperm. If an embryo doesn’t have the right number of chromosomes, it results in a failure to implant, miscarriage or (rarely) a child with a serious genetic condition. Embryos with the wrong number of chromosomes are known as aneuploid.


23 chromosomes meet 23 chromosomes to make an embryo – fertilising an egg using an intracytoplasmic sperm injection (ICSI) at CARE Fertility.


Any patient can be at risk of having aneuploid embryos. In fact, most have a mix of aneuploid and normal. The number of aneuploid embryos is known to increase as a woman gets older because her eggs are less efficient at the process of meiosis, leading to incorrect separation of chromosome pairs. For women over 37, at least half of embryos are likely to be aneuploid, and the incidence increases to almost 80% by age 43.

It is possible for embryos to be tested to see if they are aneuploid or not.  This test is called PGT-A (Pre-implantation Genetic Testing for Aneuploidy). PGT-A works by analysing segments of DNA on each chromosome to check how many chromosomes are present. In order to do this, a small number of cells are carefully removed (biopsied) from the outer layer of a blastocyst-stage embryo, and these cells are then sent to a specialist genetics laboratory for analysis. Embryos that have a normal number of chromosomes are considered suitable for transfer.


Taking a few cells from a hatching day 5 blastocyst in an embryo biopsy at CARE Fertility.


PGT-A shortens the time from treatment to successful pregnancy as it prevents transfer of embryos that are aneuploid. Embryos with a normal number of chromosomes have lower miscarriage rates and higher live birth rates per embryo transfer.


Read more​: Why should I consider PGT-A in my IVF treatment?

Rob Smith, Clinic Director of CARE London, analyses the science of PGT-A, the process of the treatment, and its benefits to patients.


We can even do PGT-A testing on embryos that are already frozen. If you have frozen embryos and wish to know if they have the potential to lead to successful treatment, they can be thawed, biopsied for PGT-A, and then re-frozen in a process called vitrification.

CARE can carry out PGT-A on frozen embryos even during lockdown, so that results are available for when we are able to undertake patient treatments again. If you are interested in PGT-A, or would like to learn more, get in touch with your CARE clinic; our team will be happy to answer all your questions.


Read more: Embryo freezing and thawing: how do we do it?

Louise Kellam, Deputy Laboratory Manager at CARE Nottingham, explains every stage of the embryo-freezing process.


Read more: The best care for your frozen embryos, eggs or sperm

Alison Campbell, Director of Embryology at CARE Fertility, explains how we diligently look after your frozen eggs, embryos and sperm in our world-class laboratories.



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