Technique boosts IVF chance of pregnancy

The low success rate of in vitro fertilisation (IVF) will be substantially improved by a new technique for counting the number of chromosomes in each cell of an early embryo, British scientists will announce today at a scientific conference.

The low success rate of in vitro fertilisation (IVF) will be substantially improved by a new technique for counting the number of chromosomes in each cell of an early embryo, British scientists will announce today at a scientific conference.

By ensuring that test-tube embryos have the correct number of chromosomes before implanting them into the womb, scientists hope to rectify the position in which even the best IVF treatment can still result in an abysmally low number of viable pregnancies.

Dagen Wells and Joy Delhanty of University College London Medical School developed the chromosome-counting technique to enable doctors to assess how many abnormal cells there are when an early embryo is at the 6-8 cell stage.

"We hope that the new technique will help embryologists to decide which embryos are the most likely to implant and develop normally. By preferentially transferring these embryos, considerably higher success rates may ultimately be achieved," Dr Wells said.

Humans have a naturally low fecundity with only a 25 per cent chance of achieving a pregnancy in each menstrual cycle even though successful fertilisation of an egg may occur in as many as 60 per cent of cycles. The difference between conception rate and birth rate is thought to be partly due to chromosomal abnormalities in early embryos, which hinder their ability to implant themselves into the wall of the womb.

By selecting those embryos with the correct number of chromosomes in each cell, embryologists hope to boost IVF success rates. Up to now, chromosome counting has been limited, with low numbers being counted in just a small proportion of the embryonic cells.

"Having a small number of abnormal cells does not automatically mean an embryo will fail to implant or that there will be a miscarriage: however, the chances of such an embryo forming a successful pregnancy are considerably less than those of a chromosomally normal embryo," Dr Wells said.

The technique, which will be given the conference prize at the American Society for Reproductive Medicine's annual meeting in San Diego this week, has been tested on 12 human embryos donated by parents having IVF treatment. Only three of the embryos were found to be completely "normal" with 46 chromosomes in all cells. Nine contained at least one abnormal cell and three contained no normal cells at all.

The findings, published in the journal Molecular Human Reproduction, demonstrate that the proportion of human embryos resulting from IVF that are completely normal is actually quite low.

Professor Delhanty said more work was necessary before the technique could be made widely available. "We are currently working on the next step - reducing the length of the procedure so that it can be applied in pre-implantation genetic diagnosis."