Developments and pregnancies of direct cleavage embryos

Abstract

The introduction of time-lapse imaging has enabled dynamic embryo observations such as cleavage-type and development-speed determinations in addition to the conventional morphological assessments. Direct cleavage (DC) represents a chromosomal abnormality rather than a normal cleavage (NC) and reportedly affects embryo development. This study aimed to investigate whether DC embryos influence the outcomes of embryonic development and single frozen-thawed embryo transfer (SFET). A retrospective study. We targeted 2614 embryos in 670 cycles from patients who underwent conventional in vitro fertilization or intracytoplasmic sperm injection between January and April 2017. After insemination, embryos were incubated in an EmbryoScope+ system (Vitrolife, Sweden). DC embryos were classified into four groups as follows: group A, abnormal embryos between the one- and three-cell stages; group B, abnormal embryos between the one-cell stage and four-cell or later stages in the first cleavage division; group C, abnormal embryos between the two- and five-cell stages; and group D, abnormal embryos between the two-cell stage and six-cell or later stages in the second cleavage division. We compared the day 3 good-quality embryo, day 5 blastocyst formation, day 5 good-quality blastocyst, and pregnancy and abortion rates after single-cycle, freeze-thawed blastocyst transfer between the DC and NC groups. The proportion of DC embryos was 24.8%. The day 3 good-quality embryo, day 5 blastocyst, day 5 good-quality blastocyst rates were respectively 74.3%, 70.9%, and 47.1% for the NC groups; 50.5%, 32.8%, and 11.1% for group A; 25.3%, 11.9%, and 0.7% for group B; 74.8%, 51.5%, and 15.8% for group C; and 48.6%, 23.9%, and 1.5% for group D. The day 3 good-quality embryo rate was significantly lower in groups A, B, and D than in the NC groups. The day 5 blastocyst rate was significantly lower in group B than in the other groups. The day 5 good-quality blastocyst rate was significantly lower in the 4 DC groups than in the NC groups. The pregnancy and abortion rates after single frozen-thawed blastocyst transfer were respectively 35.0% and 23.7% for the NC groups, 13.2% and 0% for group A, 0% and 0% for group B, 13.2% and 20.0% for group C, and 7.9% and 66.7% for group D. These parameters showed no significant differences. This study showed that the DC embryos had significantly lower day 5 blastocyst and good-quality blastocyst rates than the NC embryos. However, the DC embryos had the potential of blastocyst development and pregnancy. Thus, we suggest that DC embryos developing into blastocysts could be selected for transfer.