A groundbreaking IVF test that could improve the chances of pregnancy while almost eliminating the risk of twins or triplets is to be offered to couples in Britain for the first time.

A new genetics clinic plans to recruit between 50 and 100 women for the first trial of the procedure, which aims to identify the best embryo produced by young IVF patients with a good prognosis.

The goal of the pre-implantation genetic screening (PGS) test is to enhance success rates when only a single embryo is transplanted into the womb, to prevent multiple pregnancies that are by far the greatest hazard of infertility treatment. A different form of PGS is already licensed for detecting chromosomal abnormalities that cause embryos to fail, but only for older patients or those with a history of miscarriage or IVF failure.

It is also controversial because there is little evidence that it helps these women to conceive. The Times revealed this month that the British Fertility Society has recommended that its members stop using it.

A more advanced version of PGS, however, is now being pioneered in Britain by Dagan Wells, of the Reprogenetics UK clinic and the University of Oxford. He is seeking permission from the fertility regulator to test it on women aged under 35 who have a good prognosis. If the trial is successful, it could persuade many more infertile couples to opt for single embryos, in line with the Human Fertilisation and Embryology Authority’s strategy to cut IVF twin and triplet births from one in four to one in ten.

About 90 per cent of IVF cycles currently use two embryos, as clinics and couples fear that using only one will harm the pregnancy rates.

Dr Wells said: “I think this is going to be a wonderful thing for moving towards single embryo transfer. If you’re only going to put back one embryo, it’s more important than ever that you get the best one, and that is what we think this test can do.” The new technique has been used on three women in America, two of whom are pregnant.

PGS involves detecting chromosomal abnormalities called aneuploidies, which affect up to two thirds of embryos and cause implantation failure or miscarriage. In traditional PGS, one cell has been removed from eight-cell embryos and tested for the eight chromosomes that are most commonly defective, but this has a high error rate and the biopsy can kill the embryo.

Dr Wells’s technique relies on three new technologies that greatly improve accuracy while lowering the risk. First, a genetic screening procedure called comparative genomic hybridisation allows testing of all 24 kinds of chromosomes. Doctors are also now able to transfer embryos called blastocysts to the womb, and as these contain 100 to 150 cells, it is possible to remove several without compromising viability. This adds to accuracy, and has a higher success rate. The final development is vitrification, a freezing technique that allows embryos to be stored without damaging them.

PGS test

— The test is designed to detect aneuploid embryos, which have too many or few copies of one set of chromosomes

— Embryos will grow in-vitro for an extra two days, until they become blastocysts

— The goal is to ensure that the best embryo is selected

Sources: Reprogenetics UK; Times database

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