Corpus luteum.in pregnancy has a long life. However, if fertilisation does not take place, it remains active only for 10-12 days. Why?

Explanation

During pregnancy, there is no menstruation. The corpus luteum secretes large amount of progesterone in case the fertilisation occurs.
This is to maintain the corpus luteum as long as the embryo remains there, In the absence of fertilisation, the corpus luteum cannot be maintained for more than 10-12 days and hence, it degenerates.