For a light-hearted book, this has Major content warnings surrounding pregnancy:

past miscarriages, past stillbirths, current pregnancy in crisis, premature birth, doubt about whether mother and baby will survive the birth.

Spoiler for what happens to baby and mother:

baby is born early but in good health. Mother is at death's door and they don't think she'll make it but she does pull through. The King's grief is massive during this period while the Queen seems to be dying.