Slokam 3

Yogamaya’s cries awaken the guards and they rush to inform Kamsa of the birth of the seventh child. 

Extract from  https://indus-meetindus.blogspot.com/2015/12/Gokulam.html

Sri Krishna was born in Mathura at midnight, behind the bars, as the eighth son of Vasudeva and Devaki. Lord Vishnu appeared before them and said that he himself has born as their eighth child to rescue them and the people of Mathura. He asked Vasudeva to carry him to the house of his friend, the cowherd chief Nanda in the village of Gokul across the Yamuna, where Nanda's wife Yashoda had given birth to a daughter. Vishnu assured them that "nothing shall bar your path". He was to exchange his boy and bring Yashoda's baby daughter back to the prison.

The baby girl was an incarnation of goddess Yogmaya. Sri Nanda Gopa is also stepbrother of King Vasudeva. In order to save the child from Kamsa, Vasudeva took the child and left him in the hands of Nanda and as advised by the Lord, he hurried back to the prison of Kamsa with the baby girl. Vasudeva came back to Mathura and as he entered, the doors of the prison closed themselves. Yasoda knew that a child was born to her, but because she was tired from the childbirth, she was fast asleep. When she awoke, she could not remember whether she had given birth to a male or female child.

 Kamsa rushes to the prison,  to find his sister holding a female infant in her hands.