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With fewer and fewer embryos now replaced in each transfer cycle of IVF, embryo selection has become more important than ever.

Traditionally, embryos are chosen according to their appearance under the microscope after three or five days of development in the incubator. However, in the past few years additional techniques of selection have been introduced which use high-tech methods to screen embryos for genetic and chromosomal information.

Some studies have shown that as many as 50% of embryos are chromosomally abnormal, and, if transferred, such embryos may fail to implant in the uterus or later miscarry. The risk of chromosomal abnormalities - such as Downs syndrome - increases with maternal age.

The London Women's Clinic has begun to use new techniques of embryo analysis which indicate the chromosomal status of each embryo. The idea is that only high grade embryos without chromosome abnormalities are transferred, thus reducing the risk of pregnancy failure and improving the chances of having a healthy baby.


The technique of preimplantation genetic diagnosis (PGD) can be performed successfully in couples who are known to be at risk of passing on an inherited genetic disease to their children; however, this is a complex and demanding treatment, and appropriate only for couples known to be carriers of a genetic mutation.

PGD has revolutionised the prospects of parenthood for couples who are known carriers of, for example, the cystic fibrosis gene mutation. By identifying and transferring those embryos without the mutation, carrier couples can be reassured that their baby will not be affected by a severe genetic condition.

However, the application of the same technique as a screening measure (preimplantation genetic screening, PGS) requires a number of embryos created by IVF or ICSI and mainly tests for chromosomal abnormalities such as Downs, Edwards and Patau's syndrome.


The most commonly known technique for PGS is Array comparative genomic hybridization (aCGH), which analyses a cell from the developing embryo or the egg for the correct number of chromosomes. This test can be useful as a screening method for chromosome syndromes and other chromosomal structural changes such as translocations.

Find out more about Embryo transfer
Brentwood Hospital

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