Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).

Assertion (A): Corpus luteum is essential in maintaining pregnancy during the first trimester.
Reason (R): It secretes progesterone.

In light of the above statements, choose the correct answer from the options given below. 

If both assertion and reason are true and the reason is the correct explanation of assertion.

After ovulation, the follicle that released the egg transforms into the corpus luteum, which secretes hormones such as progesterone and estrogen. Progesterone is crucial in preparing the uterine lining for implantation of the fertilized egg and maintaining pregnancy during the early stages until the placenta takes over hormone production. It is essential for maintaining the thickened endometrial lining of the uterus and preventing menstruation during early pregnancy. Progesterone supports the growth of blood vessels in the endometrium and prepares it to support the developing embryo.