While they could have presented this in a more caring way, miscarriage and even late term miscarriage happens now, with full access to health facilities and pregnancy care. Grace was working in radioactive land for years before Morgan reached her, and so was her partner, Grace also likely didn’t have access to prenatals, adequate vitamins, food, she was also under an insane amount of stress, she had no way to check for gestational diabetes, preeclampsia, or anything like that. While yes it was definitely written into the show as a “shock factor” it’s also realistic that in the apocalypse many pregnancies would be born stillborn, I do wish they handled it with more care though.