The placenta helps in the maintenance of pregnancy by secreting a hormone,known as

Which hormones show an increased level in the maternal blood during pregnancy?

The mammalian primitive streak gives rise to

$A$: The first sign of a growing foetus may be noticed by listening to the heart sound through the stethoscope.
$R$: By the end of the second month of pregnancy,the foetus develops limbs and digits.

The eutherian placenta is derived from,or in mammals,the placenta is formed by:

Progesterone is secreted by.........