Some fertility centers are reporting slightly higher success rates with frozen embryos, including Fertility Centers of New England, which note that “Many patients are surprised that the frozen embryo transfer rates are equal to or higher than fresh embryo transfers.”
The Colorado Center for Reproductive Medicine (CCRM) believes there is an advantage to using frozen embryos. “In concordance with research at CCRM, studies from around the world have shown that in vitro fertilization pregnancies following a frozen embryo transfer are more similar to natural conception pregnancies than fresh embryo transfer cycles.” William Schoolcraft MD, medical director of CCRM says: “Since frozen embryo transfers occur a significant amount of time after a woman’s ovaries were stimulated with medications, the hormone levels in the body have had time to return to normal, which mimics a more natural conception process.”
According to Dr. Geoff Sher of Sher Fertility, a network of American fertility clinics, three developments have helped to improve the results achieved with frozen embryos:
- The introduction of ultra-rapid embryo cryopreservation (vitrification), which freezes the embryo nearly 60,000 times faster than the previously used slow freezing approach.
- The growing practice of vitrifying and cryopreserving blastocysts (embryos cultured until day 5-6) rather than early (embryos cultured until day 2-3) cleaved embryos. The practice recognises that embryos that do not develop to the expanded blastocyst stage may be chromosomally compromised.
- The introduction of full embryo karyotyping or preimplantation genetic screening (PGS) using advanced techniques. Full PGS allows embryologists to identify “competent” embryos, and these embryos can be banked over several cycles before performing the blastocyst transfer. This reduces the risk of miscarriage and chromosomal birth defects.
While some IVF doctors state a preference for frozen embryos, the selection of frozen over fresh (or vice versa) will depend on a couple’s specific case and preferences. Fertility specialists can explain the IVF process using both fresh and frozen embryos and help patients determine which option suits them best.