Which germ layer is formed first during embryonic development?

In the simplest type of placenta,the foetal blood is separated from the maternal blood by six barriers. How many barriers are lost in the human placenta?

Placenta acts like a

Placental hormone called chorionic gonadotropin $(HCG)$,which stimulates the secretion of progesterone by the ovary during pregnancy,is:

Where does the development of the embryo take place?

Women who consumed the drug thalidomide for relief from vomiting during the early months of pregnancy gave birth to children with: