After attachment of trophoblast, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus . This is called implantation and it leads to pregnancy.  After implantation, finger-like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood.The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta. The placenta facilitate the supply of oxygen and nutrients to the embryo and also removal of carbon dioxide and excretory/waste materials produced by the embryo.

Which of the following hormones are secreted by placenta ?

All of these.

The placenta is connected to the embryo through an umbilical cord which helps in the transport of substances to and from the embryo.

Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens, etc.

In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary.