Successful pregnancies after oocyte cryopreservation with slow-freezing method: a report of 3 cases

The technology for successful oocyte cryopreservation has evolved only over the past decade. Fewer than 300 pregnancies achieved with cryopreserved oocytes were reported as of the end of 2006. Two cryopreservation techniques are currently available: the slow-cooling method and vitrification. This article reviews the world literature on pregnancies conceived from cryopreserved oocytes and reports 3 such pregnancies conceived with a slow-cooling method in our facility.

Three patients who underwent in vitro fertilization/embryo transfer cycles had the supranumerary oocytes cryopreserved using a slow-cooling method. After a period of 2-7 months, the oocytes were thawed, fertilized and the resulting embryos were transferred. All 3 patients conceived and 2 delivered-1 singleton and 1 a set of twins. The third patient conceived twins and was in the third trimester of her pregnancy at this writing. Literature review indicates that the majority of pregnancies to date have been achieved with a slow-cooling protocol. However, recent advances in the vitrification technology have improved its effectiveness and because of its simplicity made it the method of choice in oocyte cryopreservation.

Both slow-freezing and vitrification methods for oocyte cryopreservation can be used effectively to achieve pregnancies. Vitrification is technically simpler and may be more effective than slow freezing.