The hormone responsible for the maintenance of corpus luteum after fertilization is HCG (Human Chorionic Gonadotropin).

Explanation:
1. Corpus Luteum Formation: After ovulation, the ruptured follicle in the ovary transforms into a corpus luteum. The corpus luteum secretes progesterone, which helps in the thickening of the endometrium and prepares it for implantation of the fertilized egg.

2. Role of HCG: If fertilization occurs, the developing embryo secretes HCG, which maintains the corpus luteum. HCG is a glycoprotein hormone that is produced by the placenta after fertilization. HCG has a similar structure to LH (Luteinizing Hormone), which is responsible for ovulation. HCG binds to the LH receptors on the cells of the corpus luteum and stimulates the production of progesterone. Progesterone helps in the maintenance of the endometrium and prevents the onset of menstruation.

3. Duration of Corpus Luteum: The corpus luteum usually disintegrates after 12-14 days if fertilization doesn't occur. However, if fertilization occurs, the corpus luteum is maintained by HCG until the placenta takes over the production of progesterone.

Conclusion:
Thus, the hormone responsible for the maintenance of corpus luteum after fertilization is HCG. HCG binds to the LH receptors on the cells of the corpus luteum and stimulates the production of progesterone, which helps in the maintenance of the endometrium and prevents the onset of menstruation.