As Kitty's labor continues, Levin is completely distraught, caught up in this ecstatic state of waiting. He wants Kitty's suffering to end, and doesn't recognize either Kitty's screams or her distorted, pained face.
Finally, the baby has been delivered, and it's all over.
The midwife tells him that the baby is a healthy little boy.
The child starts shrieking, and Levin doesn't recognize at first that those cries are coming from his child.
Levin is filled with delirious joy. Here is this new person, his son, whom he has to get to know. He can't immediately understand the idea that a child who wasn't here the day before has sudden materialized in his life.