Recent improvements in cell culture systems have led to a shift in in vitro fertilization (IVF) practice from early cleavage stage embryo transfer (ET) to blastocyst transfer. Blastocyst culture and transfer could theoretically provide better synchronization between the embryo and the uterine endometrium. The purpose of this study is comparing pregnancy rates and implantation rate following transfer of thawed cleavage embryos and blastocysts cultured from thawed cleavage embryos.

The proposal of this study approved by our institutional review boards and institution's ethical committee, and all participants will sign a written consent before enter to study. All patients will be randomly divided into two groups of thawed cleavage embryo transfers and transfers of blastocysts from thawed cleavage embryos. Embryos will be transferred in hormone replacement cycles. Preparation of the endometrium will be started in the second day of menstruation and will be continued according to their transfer type (blastocyst or cleavage). βhCG will be assessed 14 days after embryo transfer. Treatment cycle outcomes will be compared between 2 groups.

Inclusion Criteria:

• The patients with first type of infertility
• Age ≤ 37 years
• Long ovulation induction protocol

Exclusion Criteria:

• Any previous surgery on the uterus and ovaries
• Uterine factor infertility
• Sever Male factor infertility (TESE, TESA ،Oligoteratozoospermia)
• Recurrent abortion
• The women with poor ovarian reserve