研究開発・学会発表

Study Question
Does the reduced number of blastomeres, caused by the cryopreservation and the thawing procedures of 4-8 cell stage embryos, affect in vivo embryo development and take-home baby rates?

Summary answer
There was no difference between intact embryos and embryos with less than 25% of cellular damage on pregnancy rates and birth rates.

What is known already
Some reports demonstrated that similar implantation rates were obtained between intact early stage embryos cryopreserved on day 2-3 and those embryos with less than 25% cellular damage after slow freezing and thawing procedures. It is known that there are higher survival rates using the vitrification procedure, as opposed to the slow freezing procedure, for early cleavage stage embryos. The birth rates of partially damaged embryos have not yet been reported.

Study design, size, duration
A retrospective study has been conducted from January 2010 to December 2013 on the survival rates of 1549 vitrified and thawed embryos, which were cryopreserved on day 2.

Participants/ materials. Setting, methods
Embryos were divided into four groups (intact embryos, embryos with less than 25% cellular damage, 25%-50% damage and more than 50% damage). The relationship between cellular damage and pregnancy rates was analysed in the 1549 single embryo transfers. The birth rates of 1491 cases were assessed by questionnaire.

Main results and role of chance
The biochemical pregnancy rates in 0%, <25%, 25-50% and >50% of cellular damage groups were 35.1% (460/1309), 34.4% (43/235), 26.2% (16/61) and 28.6% (4/14) respectively. The rates of gestational sac confirmation in each group were 21.1% (277/1309), 19.2% (24/125), 11.5% (7/61) and 7.1% (1/7). The fetal heartbeat rates in each group were 18.3% (239/1309), 19.2% (24/125), 9.8% (6/61) and 7.1% (1/14). The birth rates in each group were 15.1% (196/1299), 13.4% (16/119), 8.5% (5/59) and 7.1% (1/14). There was no difference between 0% and <25% groups within each parameter. When the cut-off volume of damage was defined as <25%, the rates of gestational sac confirmation and fetal heartbeat were significantly higher in embryos with <25% cellular damage than those with >25% damage (p=0.047 and p=0.030).

Limitations, reasons for caution
A limitation of this study is that the number of embryos in the >50% group was insufficient to provide enough data for accurate study. To improve the accuracy of the data, it is necessary to perform a long-term study in the future.

Wider implications of the findings
The results suggest that embryos with less than 25% damage have the same potential to result in birth as an intact embryo. This study also demonstrated that a baby could be born from an early cleavage embryo with over 50% blastomere damage.