AMSTERDAM — A new genetic screen of zygotes performed a few hours after in vitro fertilization has advantages over conventional preimplantation genetic screening, particularly in patients with a very poor prognosis, based on results of the first clinical application of the procedure.
Although preimplantation genetic screening (PGS) allows examination of only about half of the chromosomes in a 3-day embryo, the new technique, known as comparative genomic hybridization (CGH), can evaluate all chromosomes in newly fertilized oocytes (zygotes), Elpida Fragouli, Ph.D., reported at the annual meeting of the European Society of Human Reproduction and Embryology.
Her study of CGH in 82 women with a very poor prognosis shows an ongoing pregnancy rate of 20%, including three deliveries.
“This is exceptional considering the extremely poor prognosis of the women involved,” said Dr. Fragouli of the University of Oxford (England). “This represents a doubling of the usual pregnancy rate for people who fall into this category, which is otherwise, at best, under 10%, and at worst, 0.”
The women were an average of 41 years old, with histories of implantation failures and multiple unexplained spontaneous abortions, she said.
Using CGH, Dr. Fragouli and her associates found chromosomal abnormalities in 64% of 473 screened zygotes, including abnormalities in chromosomes that are not examined in conventional PGS. “With standard screening, 39% of these abnormalities would not have been detected, and 16% of abnormalities would have been incorrectly diagnosed as normal.”
Only healthy zygotes were allowed to mature, resulting in 73 embryos, which were transferred to 35 patients.
The CGH technique is considered less invasive than regular PGS, because it does not require a day 3 biopsy of embryonic cells, which some experts consider damaging to the embryo. Instead, CGH involves the removal and examination of polar bodies, which are by-products of fertilization and not necessary for embryo development.
Dr. Fragouli did not declare any conflicts of interest.