Fair Mary of Wallington or Fair Lady of Wallington (Roud 59, Child 91) is a traditional English-language folk ballad.
[1] Francis James Child lists at least seven variants of the ballad.
She dies; in most variants, the baby has to be saved by cutting open her side.
[4] A Breton ballad, Pontplancoat, appears too similar in form to this not to be from a common source: Pontplancoat marries a woman named Marguerite as his third wife.
Marguerite died, and the baby was saved by cutting open her side.