Glujovsky D, Riestra B, Sueldo C, Fiszbajn G, Repping S, Nodar F, Papier S, Ciapponi A.

Vitrification versus slow freezing for women undergoing oocyte cryopreservation.

Cochrane Database of Systematic Reviews 2014, Issue 9. Art. No.: CD010047. DOI: 10.1002/14651858.CD010047.pub2.

Review question: What is the effectiveness and safety of vitrification in comparison to slow freezing as a method of preserving oocytes (eggs) in women undergoing assisted reproduction?

Background. Oocyte cryopreservation is a technique with considerable potential in reproductive medicine, including to preserve fertility, as a way of delaying childbearing, and as part of oocyte donation programs. Although the technique was relatively ineffective at first more recently numerous modifications have led to higher success rates. Cochrane review authors evaluated the evidence on two methods of freezing oocytes, vitrification and slow freezing. The most important difference between the techniques is the speed of freezing the eggs. Vitrification is a faster process which may potentially cause less damage to the eggs.

Characteristics of the included studies. The search of the medical literature was done in March 2014. We found two randomised controlled trials (RCTs) with 106 participants comparing oocyte vitrification versus slow freezing. Neither study reported live births or adverse events as outcomes. One reported ongoing pregnancy and both reported clinical pregnancy.

Key results. The clinical pregnancy rate was higher in the oocyte vitrification group than in the slow freezing group. The effect of vitrification compared to slow freezing on ongoing pregnancy rates was only reported in the one small study, with inconclusive findings.

Quality of the evidence. The quality of the evidence was rated as moderate for clinical pregnancy and low for ongoing pregnancy. The evidence was limited by imprecision.