פּירוש אויף שמואל ב 6:23

“Michal, the daughter of Saul had no children” [6:23]. Michal did not have any children, but she would die if she had a child. There are three women who died in childbirth. The first was Rachel, the wife of Jacob. The second was the daughter-in-law of Eli the priest. The third was Michal, as is written about all three.⁷B. Sanhedrin, 21a.

Had no child From that day on.¹²Prior to that day, she did have a child, Yisroam mentioned earlier (Shmuel II, 3:5), see Rashi there.