Corpus luteum in pregnancy has a long life. However, if fertilisation does not take place, it remains active only for 10-12 days. Why?
During pregnancy, there is no menstruation. The corpus luteum secretes large amount of progesterone in case 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 more than 10-12 days leading to its degeneration.