Higher Miscarriage rate with vitrification than with Slow Freezing in a prospective study with sibling embryos.

Introduction: Survival rate of vitrified oocytes and embryos is considered to be higher than with slow freezing.

Aim: to compare the outcome of freezing thawing by vitrification with slow freezing in sibling oocytes

Materials and methods: From February 2008 to December 2012, cycles ≥5 or more supernumerary D2, D3 embryos suitable for freezing were randomized into: Group A- slow freezing using the standard embryo freezing kit (Origio-Medicult). Group B- vitrifiction utilizing vitrification cooling kit (Origio- Medicult). Thawing or warming was performed during 2008 to December 2016. Thawing or warming in the first cycle was matched by computer. Day 2 embryos were cultured overnight Thawed or warmed embryos were incubated for 2-4 h before transfer. Only intact or embryos with ³50% viable blastomeres were transferred on day 3 after LH surge, or following three days of progesterone intake. Embryos were thawed or warmed till the achievement of 1-3 good quality embryos, suitable for transfer. The outcome of the thawed and warmed sibling embryos was compared for survival, pregnancy, multiple pregnancies miscarriages and implantation rates.

Results: There were 163 thawed/warmed cycles in which sibling embryos were transferred at the time to the same patient. In 15 group A cycles and in 2 group B cycles none of the thawed/warmed embryos survived. Thus, their sibling vitrified or frozen embryos were thawed/warmed and transferred. Patients’ age was 30.4±4.9 years. 37% (204/549) of the embryos in group A were intact and 77% (341/441) in group B, p<0.001. The overall survival rate (intact embryos and embryos with ³50% viable blastomeres) was 72% (397/549) and 95% (421/441), p<0.001 respectively. 2.5±0.7 group A embryos and 2.4±0.6 group B ones were transferred. Implantation rate was 14.5% and 18.0%, respectively (NS). Clinical pregnancies rate per ET was 33.1% (49/148) and 35% (56/161), NS. Multiple pregnancies were 10% in group A and 25.0% in group B; p<0.05. 18% miscarried among group A pregnant patients and 34% in group B patients (p<0.05). 18% in group A was significantly lower (p<0.05 Fisher`s exact test) than in group B 34%. Ongoing pregnancy rate (>8 week) was 27% in group A and 23% in group B (NS).

Conclusions: This study demonstrates a significant increase in intact embryos and overall survival rates with vitrification. Since equal qualified embryos were transferred in both groups, pregnancy and implantation rates were comparable. However, more miscarriages were found in the vitrification group which leaves the ongoing pregnancy still comparable.