(CNSNews.com) -- A new study by the Center for Human Reproduction in New York published August 11 by the Journal of the American Medical Association finds that delaying motherhood by freezing eggs (oocytes) could actually harm a woman’s chance of having a successful birth.
Many fertility experts recommend egg freezing, or cryopreservation, to women who wish to delay having children until later in life because implantation of younger eggs has shown to result in more successful pregnancies.
However, the new study suggests that frozen eggs (cryopreserved oocytes) produce significantly lower in-vitro birth rates than donor cycles using fresh oocytes.
“The reasons for lower live birth rates with the use of cryopreserved oocytes remain to be established,” says the research letter. “One possible explanation is less opportunity for proper embryo selection due to smaller starting numbers of oocytes, leading to fewer embryos available for transfer.
“Alternatively, oocyte quality may be negatively affected by cryopreservation and thawing,” the letter continues.
The study compared live birth rates using either fresh or cryopreserved eggs in 91.7 percent of all donor IVF (in-vitro fertilization) cycles in the U.S. in 2013, which included data from 81.4 percent of the 467 fertility centers in the U.S.
The findings show that women had a 56 percent chance of becoming mothers with IVF embryo transfers that used fresh eggs, but only a 47 percent chance with frozen eggs.
The figures suggest that nine out of every 100 women whose IVF treatment includes cryopreservation may not become mothers, but the researchers warn that their findings should be treated with caution because they could not adjust for the age of the mothers or their infertility diagnoses because data from the clinics was anonymised.
IVF, one of several assisted reproductive technologies (ART), is the process by which an egg and sperm are manually combined in a laboratory dish. The resulting “test tube” embryo is then transferred to the uterus, according to the American Pregnancy Association.
According to the Centers for Disease Control and Prevention (CDC), “approximately 1.5% of all infants born in the United States are conceived using ART.”
But the procedure remains controversial for ethical, legal and medical reasons.
The typical IVF process creates more human embryos than donor couples desire, so there are now an estimated 600,000 human embryos frozen in storage facilities throughout the U.S., according to Nightlight Christian Adoptions, which tries to find couples to adopt these "snowflake" babies.
But hundreds of thousands of frozen human embryos still remain in "legal limbo", according to Christopher White, director of research and education at the Center of Bioethics and Culture.
IVF also comes with medical risks.
According to a 2012 study published in Fertility and Sterility, IVF babies have a 37 percent higher risk of being born with a birth defect compared to naturally conceived children.
And a 2014 study of more than 300,000 births in Australia by researchers at Adelaide University found that women giving birth via IVF were five times more likely to suffer complications.
In addition, women who used fertility treatments to conceive doubled their risk of having a premature, stillborn or seriously underweight baby, researchers found.