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Evidence Challenges Effectiveness Of Embryo Screening For Older Women

There is growing evidence that a procedure for identifying chromosomal abnormalities in embryos prior to in vitro fertilization is ineffective at helping older women become pregnant, the Wall Street Journal reports. The procedure -- known as pre-implantation genetic screening, or PGS -- is performed in dozen of U.S. fertility clinics and sometimes marketed to older women as a way to increase the odds of a healthy live birth. PGS involves extracting a single cell from a six-cell embryo and inspecting it for chromosomal abnormalities known as aneuploidies; unaffected embryos can then be implanted through IVF. Women older than age 35 have a higher risk of aneuploidies, in which embryos have fewer or more than the usual number of 23 pairs of chromosomes. Aneuploidies can trigger early miscarriage or certain genetics conditions, such as Down syndrome. Most medical experts agree that embryo screening is capable of significantly reducing the risk of Down syndrome and other serious chromosome-related illnesses. However, evidence from several studies increasingly suggests that the procedure does not increase older women"s chances of healthy live births. The American Society for Reproductive Medicine released an initial opinion about PGS in 2007, saying that available evidence does not support the use of embryo screening to increase live birth rates in older women. Andrew La Barbera, scientific director of the society, said, "Since that time, there have been several more trials that have reached the same conclusion." Another shortcoming is that most clinics can only test for fewer than half of the 23 chromosomes, meaning that many defects can go undetected. However, medical experts say that the use of PGS has increased in the two years since ASRM issued its recommendations. According to the Journal, PGS can add more than $2,000 to the roughly $10,000 cost of one IVF cycle. Very few health insurers cover PGS, though some pay for IVF. Some experts contend that studies showing a lack of clinical benefit from PGS do not use more efficient biopsy techniques that can prevent damage to the embryo. Santiago Munne, scientific director for Reprogenetics, said that the treatment is "effective." In a 2007 study, Munne and colleagues used PGS to reduce the rate at which patients miscarried. However, the chances of a woman getting pregnant largely were unchanged, which the authors said could be attributed to the small number of study participants (Naik, Wall Street Journal, 6/1).

Study Rewrites Textbook On Key Genetic Phenomenon

Because females carry two copies of the X chromosome to males" one X and one Y, they harbor a potentially toxic double dose of the over 1000 genes that reside on the X chromosome.