(RxWiki News) The process of in vitro fertilization (IVF) involves a series of complex steps to coax a woman's body to produce extra eggs for fertilization and implantation.
A fertility conference presentation has investigated whether implanting fresh embryos during the same cycle when a woman's eggs are extracted is more or less effective than implanting frozen ones during a different menstrual cycle.
"Discuss IVF embryo transfer options with your doctor."
Professor Miguel Angel Checa, of the Department of Obstetrics and Gynecology at the Hospital Universitari del Mar within the Universitat Autonoma de Barcelona in Spain, and colleagues conducted a review of the literature on cryopreservation methods and options with embryos.
"Cryopreservation" is the term for saving and preserving a woman's eggs by freezing them while waiting to fertilize them and implant them during IVF.
Based on all the studies reviewed by the researchers, it appears that women have a 30 percent greater chance of achieving a pregnancy following IVF implantation if they freeze all their eggs initially and then have an embryo transplanted later - after their cycle involving the eggs' removal.
The reason is related to the way a woman's body is prompted to produce viable eggs. IVF involves an intensive process that prepares the woman's body to release more eggs than she normally would during ovulation.
Typically, a woman ovulates one or two eggs at a time from her ovaries. But fertility doctors need more eggs so that they can be sure there are enough viable ones available to fertilize and implant. Then they freeze the extra ones.
Women take follicle-stimulating hormone (FSH) to stimulate their ovaries to release extra eggs, which are then extracted and evaluated by fertility doctors.
Usually, one or two of these eggs are immediately fertilized with sperm and implanted in the woman very soon after the eggs have been taken out.
However, the process of stimulating the ovaries has been shown to have problematic effects on a woman's endometrium, the inner layer of the uterus, which could make it more difficult for the fertilized embryo to successfully implant.
When the ovaries produce multiple eggs at once, they also release more of a hormone called estradiol, which can affect how receptive the endometrial tissue is to an egg. Researchers have also seen DNA pattern changes in the endometrium following ovarian stimulation.
Further, transplanting an embryo immediately after extracting the eggs in the same cycle can increase the risk of a woman's developing ovarian hyperstimulation syndrome, a painful and potentially dangerous condition in which the ovaries swell and fluid leaks into the belly.
If all a woman's eggs were frozen and stored until the effects of the ovary stimulation have passed and a woman's new cycle has begun, the researchers theorized, it's possible that her chances of a successful implantation could occur and that her risk of ovarian hyperstimulation syndrome would drop.
Because no systematic studies had compared the success of frozen embryo transfers with fresh embryo transfers, the researchers combed the literature and determined that the evidence together confirmed their hypothesis.
The review included 64 studies, three of which were randomized trials, that were published before December 2011 and involved 633 IVF/ICSI cycles.
ICSI, or intracytoplasmic sperm injection, is the process of injecting sperm into an egg outside of the woman's body to create an embryo for transplantation.
There were 316 cycles involving transplantation of fresh embryos and 317 of frozen embryo transfers. The data revealed that the likelihood of a pregnancy was about 1.31 times higher with a frozen embryo.
While 38 percent of the fresh embryo transfers resulted in a pregnancy, 50 percent of the frozen embryo transfers led to a pregnancy. There were no differences in miscarriage rates between the two types of transfers.
"The pooled data demonstrates that embryo cryopreservation and subsequent frozen embryo transfer may improve the outcome of assisted reproduction treatment," said Checa.
Because these results are preliminary and there is still little data available, Checa said doctors should wait to see what currently ongoing studies reveal regarding fresh versus frozen embryo transfers.
"We are quite confident with our results," he said. "But in our view we should wait until the end of the year for results from other studies to confirm our data and recommend a change in IVF policy."
If the studies do confirm that frozen embryo transplantation is equally or more effective than fresh embryo transfers, then fertility doctors could consider making it standard procedure to freeze all eggs after extraction and wait until a woman's next cycle - after the effects of stimulating her ovaries have passed - before implanting an embryo.
"When we freeze all of the embryos, we completely avoid the risk of ovarian hyperstimulation syndrome," said Professor Checa. "So freezing all the embryos we collect would avoid the biggest complication that exists in assisted reproduction."
The study was presented July 4 at the 28th annual meeting of the European Society of Human Reproduction and Embryology in Istanbul.
Because the study has not yet been published in a peer-reviewed journal, its results should be regarded as preliminary and still require review by researchers in the field. No information was available regarding funding or disclosures.