Testing of fertilized eggs that undergo in-vitro fertilization treatment to identify genetic diseases before pregnancy has reduced the rate of miscarriages in women who had repeatedly miscarried, a large-scale clinical trial has found.

The Japan Society of Obstetrics and Gynecology, which analyzed the clinical trial covering 9,097 people at 200 facilities, concluded the method proved to be effective in reducing the miscarriage rate in results released Sunday.

In the trial, the society analyzed women who had suffered miscarriages repeatedly or had not become pregnant even after transplanting fertilized eggs in their wombs multiple times.

The miscarriage rate of transplanted fertilized eggs without abnormalities in chromosome was roughly 11 percent, lower than the miscarriage rate of some 25 percent involving typical IVF treatment in Japan.

In the meantime, the actual birth rate with the testing was estimated to be around 25 percent, almost the same as that of typical IVF treatment cases, indicating the testing is unlikely to contribute to a rise in the number of births.

It is believed that even if a fertilized egg with an abnormal chromosome is implanted without the testing, the abnormality may be repaired in utero in some cases and lead to its birth, according to the society.

Preimplantation genetic testing, which examines chromosomes of fertilized eggs, was first approved by the society in 2004 at the request of people concerned about the possibility of passing on a genetic trait that could cause serious genetic diseases.

The society crafted in January this year new guidelines to conduct preimplantation genetic testing involving counting chromosomes comprehensively for women who suffered miscarriages two more times at facilities approved by the society, with the aim to reduce miscarriages and improve birth rates.

But the testing has often been met with criticism since it could lead to only fertilized eggs without abnormalities being selected as worthy of life, even though it is intended to prevent miscarriages.

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