Abstract: Objective：To study the effect of in vitro fertilization-embryo transfer (IVF-ET) on the expression of the gene of phosphate and tension homology deleted on chromsome ten (PTEN) and its protein in the placenta villus and embryonic tissues. Methods：Eight cases undergoing IVF-ET and the ultrasound-guided embryo reduction (the IVF-ET group), and 10 cases of natural pregnancy undergoing abortion (the control group) were included in this study. The placental villus and embryonic tissue were collected. The expression of PTEN mRNA was measured by real-time qPCR. The distribution of PTEN protein in tissues was tested by immunohistochemistry. Results：PTEN protein was expressed in the cell membrane and cytoplasm of placental villus trophoblast cells and syncytiotrophoblast cells, and widely expressed in the different germ layers of early embryo. The expression of PTEN protein in the placental villus of the IVF-ET group was lower than that of the control group (t=2.325, P=0.027). However, there was no significant difference in the expression of PTEN protein in the tissues of early embryo between the two groups (P=0.288). The expression pattern of PTEN mRNA was just consistent with that of PTEN protein. Conclusions：The in vitro procedure of IVF-ET may decrease the expressions of PTEN gene and protein in placenta, however does not change the expression levels in the tissues of early embryo. It is necessary to explore the underlying meanings of the decreased PTEN expression in placenta related to IVF-ET.

Key words: Fertilization in vitro, Embryo transfer, Placenta, PTEN, Embryo