At 44 years old -- five years after successful treatment for large b-cell non-Hodgkin's lymphoma -- Molly Allen gave birth to her fifth child, a son named Max.

"After my lymphoma treatment, the doctors warned me I probably wouldn't be able to get pregnant, but I felt like we were meant to have another child," she says. As time passed though, I had almost given up on having another biological child and was thinking about...