The use of frozen eggs, or oocytes, for in vitro fertilization leads to lower live birth rates than the use of fresh eggs. This is the finding of a new study published in JAMA.
Traditionally, fresh oocytes that have been donated for in vitro fertilization (IVF) have been used for fertilization straight away. The created embryos can be transferred into the uterus immediately or frozen (cryopreserved) for use at a later date.
In recent years, however, oocyte cryopreservation has grown in popularity, in which a woman's eggs are extracted, frozen and stored. When a woman decides she is ready to become pregnant, the eggs can be thawed and fertilized via the standard IVF procedure.
A number of studies have suggested the success rates of IVF with frozen eggs are comparable to those of IVF with fresh eggs. As such, the American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) published a joint guideline in 2013 declaring that oocyte cryopreservation "should no longer be considered experimental."
However, before universal oocyte cryopreservation can be recommended, the ASRM-SART guideline called for "more widespread clinic-specific data on the safety and efficacy" of the technique.
Still, some fertility clinics in the US have introduced frozen donor egg banks, encouraged by research indicating IVF using oocyte cryopreservation is just as successful as traditional IVF.
In this latest study, Dr. Vitaly A. Kushnir, of the Center for Human Reproduction in New York, NY, and colleagues set out to assess outcomes of IVF using oocyte cryopreservation in routine clinical practice - something the team says has not previously been investigated.
7% lower live birth rate with oocyte cryopreservation
The researchers analyzed 2013 data from 380 fertility centers in the US. These centers performed 92% of all IVF cycles in the country that year, according to the authors.
The team identified 11,148 oocyte donation cycles, of which 2,227 (20%) involved the use of cryopreserved oocytes, and the live birth rates of each IVF technique were compared.
- In the US, 1 in 8 couples have problems getting pregnant or sustaining a pregnancy
- Around 7.4 million women in the US have ever received infertility services in their lifetime
- Less than 3% of infertility cases in the US are treated with assisted reproductive technologies such as IVF; around 85-90% of cases are treated with surgical procedures or medication.
The results of the analysis revealed that live birth rates with the use of oocyte cryopreservation for each completed IVF cycle were lower at 43%, compared with 50% with the use of fresh oocytes.
For each embryo transfer, live birth rates were 47% with the use of frozen oocytes and 56% with the use of fresh oocytes.
While the researchers are unable to pinpoint the exact reasons for lower live birth rates with the use of oocyte cryopreservation, they hypothesize that it may be down to the reduced amount of eggs used for this IVF procedure.
"In traditional donor egg therapy (using fresh eggs), the recipient gets all the eggs the donor makes (typically 15-25)," James Toner, president of SART, explained to The Washington Post. "When frozen eggs are employed, only a batch of 6-8 eggs are provided. This has a big effect on outcomes!"
In addition, Dr. Kushnir and colleagues say it is possible that oocyte quality could be compromised during the freezing and thawing process.
They stress, however, that their research should be "viewed with caution," noting that they did not account for potentially confounding factors, such as the age of egg donors and recipients and infertility diagnosis.
Elsewhere on Medical News Today, a new study published in the Journal of Endocrinology suggests retrieving oocytes earlier in the IVF process may improve success rates for older women.