October 16, 2010

First Babies Born In IVF Genetic Screening Trial

Two women have given birth to three healthy babies from eggs screened for genetic defects prior to in-vitro fertilization, the European Society of Human Reproduction and Embryology (ESHRE) announced on Friday.

The babies, twin girls born in Germany in June and a boy born in Italy in September, are the first deliveries in the controlled pilot study, which is the first of its kind anywhere in the world.

The new screening technique, known as comparative genomic hybridization (CGH) by microarray, could one day improve IVF success rates by screening oocytes for a full range of chromosomal disorders, the doctors said.

The study was conducted in Italy and Germany, and was designed to determine the clinical value of CGH as a non-subjective means of genetic screening prior to embryo transfer.

"All the babies and their mothers are doing very well in terms of weight and overall developmental performance," said embryologist Dr. Cristina Magli of the SISMER Center in Bologna, Italy.

The births, as well as several ongoing pregnancies in the study group, are the final stage of the "proof of principle" that screening oocytes and embryos before IVF transfer can increase birth rates.

"We have learned from more than 30 years of IVF that many of the embryos we transfer have chromosome abnormalities," said ESHRE's chairman Luca Gianaroli.

"Indeed, it's still the case that two out of every three embryos we transfer fail to implant as a pregnancy, many of them because of these abnormalities."

"The whole world of IVF has been trying to find an effective way of screening for these abnormalities for more than a decade, but results so far have been disappointing with the technology available. Now we have a new technology in array CGH and our hopes are that this will finally provide a reliable means of assessing the chromosomal status of the embryos we transfer," she said.

Human cells have 46 chromosomes, 23 from each parent. Before an egg is fertilized, it ejects half of its full set of chromosomes to make room for the 23 coming from the sperm.  These discarded chromosomes, held in a structure known as a "polar body," are a mirror image of those remaining in the egg.

The microarray CGH technique evaluated in the study offers several advantages over other screening methods, ESHRE said in a press release about the study.

With polar body CHG, all 23 pairs of chromosomes in a cell are tested, instead of just a limited number.  Furthermore, since the cell being tested (the polar body) is obtained from an oocyte at fertilization, there is no need to obtain the biopsy of a cell from a developing embryo for analysis.  Previous chromosome tests were conducted on cells biopsied from growing embryos, and did not necessarily reflect the total status of the embryo.  

Additionally, while CGH tests on biopsies from five-day-old embryos require several days to deliver complete results -- requiring the freeze-storage of the embryo before it can be transferred -- polar body CGH can be done in real time and does not require freezing.

Finally, since polar body CGH is conducted on oocytes, not embryos, nations such as Germany that outlaw embryo analysis and freezing will have reliable method of pre-implantation genetic screening.

ESHRE said that because the chromosomal status of the transferred embryo can be accurately predicted with CGH, doctors can select an embryo with the best chance of progressing to a live birth, reducing the need to implant multiple embryos.

In the short term, the IVF patients most likely to benefit from polar body CGH screening are those of an older maternal age (over 37 years), those with a record of unsuccessful IVF, and those with a history of miscarriage, ESHRE said.

All of these conditions are associated with a higher than average rate of embryonic chromosomal abnormality.

"The study has already caused huge interest in the scientific and clinical community," said Dr. Magli.

"We are very proud to announce these results. It is the first time that a scientific society like ESHRE has organized a study to determine the clinical value of a technique which could prove a revolution in IVF."

The next step for ESHRE will be to upgrade the pilot study into a large-scale international clinical trial, which is planned for next year, the society said.


On the Net: