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Egg Freezing Before IVF Not Harmful for Pregnancy Rates
a blog by Claire, September 14, 2012
Embryos created from eggs (oocytes) that have been frozen (vitrified) have a similar chance at achieving a pregnancy as those created from fresh eggs, finds a new study conducted by Reproductive Medicine Associates of New Jersey (RMANJ). In addition, the embryos are not at increased risk of aneuploidy (abnormal number of chromosomes). The study was published in the September 2012 issue of Fertility & Sterility.
"This study was the first well-controlled clinical trial of the impact of oocyte vitrification on embryo development and clinical outcome," says Richard T. Scott, Jr., M.D., FACOG, HCLD, founding partner of RMANJ. The randomized controlled was designed to assess the impact of egg freezing on aneuploidy and reproductive potential by comparing frozen and control oocytes from a single patient within a single cycle and a single fresh transfer. The study included 44 patients with a mean age of 29.9 +/- 2.3 years who had normal ovarian reserve.
The researchers measured the rate of aneuploidy, as well as fertilization, cleavage, blastulation, and implantation in embryos created from frozen and control eggs.
Out of a total of 588 mature oocytes, there were 294 that had been frozen, and 240 of those survived thawing. Among surviving frozen eggs, there was no difference in the rate of embryonic aneuploidy In paired blastocyst transfers (vitrified, 29.1 percent vs. control, 26.4 percent). In addition, the ongoing pregnancy rate per embryo was comparable (vitrified, 53.9 percent vs. control, 57.7 percent). There were, however, differences noted in embryonic development. There was a lower fertilization rate with intracytoplasmic sperm injection (ICSI) (vitrified 77.9 percent vs. control 90.5 percent), a lower cleavage rate (vitrified 90.9 percent vs. control 99.2 percent), and a lower usable blastocyst formation rate per two pronuclei (vitrified 34.8 percent vs. control 50.8 percent).
The study is important because it demonstrates several things for women who freeze their eggs for either medical or social reasons:
- Embryos produced from frozen eggs are not at an increased risk of chromosomal abnormalities.
- Embryos produced from frozen eggs are just as likely to implant, and the women are just as likely to have a successful pregnancy.
- With embryos created from frozen eggs, there is no need to increase the number of embryos transferred.
"This study provides an important piece of safety data that had been missing from the egg freezing story, namely that the embryos produced after vitrification are not at an increased risk of being chromosomally abnormal and are just as likely to implant and deliver healthy newborns," says Eric J. Forman, M.D., the lead investigator on the study. "Women who have to delay reproduction for a variety of reasons — including prior to chemotherapy for cancer — can for the first time do so with security, knowing that the embryos that develop later are just as likely to be normal. With very high implantation rates, you don't need to transfer more embryos. These women can take advantage of all the benefits of single blastocyst transfer even if they are at an advanced reproductive age when they are ready to use the frozen oocytes."