Clair Sudron, 32, was diagnosed with breast cancer two years ago and had surgery to remove a lump, while chemotherapy killed any remaining cancerous cells.
She had prepared herself for a life without children after doctors had warned her that, after four courses of the treatment, she would probably be left infertile.
But a year later, she discovered she was pregnant - and she gave birth to daughters Bella and Scarlett Herring seven weeks ago.
Clair, who lives with partner Steven Herring in Hartlepool, told her local paper: "I had all of the symptoms of being pregnant but to be honest I thought it was the chemotherapy, it really messes all of your systems up.
"But I did a few tests and they were all positive.
"I remember ringing my family and telling them I was going round to speak to them, they all thought I was going to tell them the cancer had came back.
"I had always wanted to have kids but I just figured I was going to have to have get used to the idea of not being able to.
"To find out I was pregnant and then to find out I was going to have twins was fantastic, absolutely fantastic."