The first human birth from a frozen oocyte was reported in 1986. Almost three decades later, mature oocyte cryopreservation has emerged as a meaningful technology to preserve reproductive potential in women. The American Society for Reproductive Medicine (ASRM) removed the “experimental” label from egg freezing but cautioned that more data on safety and efficacy were needed prior to widespread adoption of the technique in 2013.
Vitrification and Slow Freezing: How did we get here and how effective are they?
Fertility preservation is a continually advancing field in reproductive medicine. Cryopreservation refers to the cooling of cells to subzero temperatures, which stops biologic activity and preserves the cells for future use. Clinically, oocyte cryopreservation requires the patient to undergo in vitro fertilization (IVF). “Cryo” originated from the Greek word “kryos” which means icy cold. Cryopreservation is not a new science. In 1776, the Italian priest and scientist Lazzaro Spallanzani reported that sperm became motionless when cooled by the snow. In 1949, an English scientist, Christopher Polge, showed the glycerol, a permeating solute, could provide protection to cells at low temperatures. After that, sperm cryopreservation advanced quickly, partially because of the ease of observing sperm motility. The first birth using human cryopreserved sperm took place in the 1950s and the first human birth after embryo thaw occurred in 1983. Since then, cryopreservation has been seen as a cornerstone in the field of reproductive medicine.
Initial problems encountered with egg freezing:
Even though the first birth from a thawed human oocyte took place in 1986, there were still many technical difficulties. Oocytes proved challenging to successfully cryopreserve. The water crystals formed by ice caused damage as well as the rising concentrations of intracellular solutes as cells cooled to freezing. The high water content of the human oocyte made it susceptible to the negative effects of freezing. Freeze-thaw hardening of the zone pellucida leads to decreased postthaw fertilization. The meiotic spindle is extremely delicate and prone to injury from ice crystals.
More to come on this topic next month!