Abstract: The placenta is an important communicating organ between the mother and the fetus, and its normal development is crucial for the growth and development of the fetus. The formation and development of placenta is greatly relevant to some factors, such as gender, epigenetics and external environment. For example, the gender affect the expression of sex hormone genes in male or female fetal placenta respectively, and the sex hormone synthesis gene STS in X-linked genes tends to express in female fetal placenta. Moreover, the expression of LHB-CGB gene cluster also tends to express in female fetal placenta, and its expression products such as luteinizing hormone and hCG are closely related to the growth, invasion and angiogenesis of placenta. On the other hand, the reconstructive process of methylation in epigenetics affects the early development of placenta, such as the inhibition of DNA methylation during early embryonic development can disrupt the proliferation and migration of trophoblasts. In addition, the growth of placenta requires a hyperoxic environment, and the decline of oxygen level can directly impair placental volume, development and maturation by inducing increases in the activity of hypoxia-inducible factor (HIF). To review a series of changes during placental development and their effects on the varied physiological functions, such as epigenetics and changes of vascular structure, are essential for elucidating the mechanism of embryonic development and the maternal and infant safety as well.

Key words: Placenta, Epigenesis, genetic, Sex factors