A US mother told by her doctor she would miscarry has expressed joy at her daughter’s survival against all odds.

In a post to the Love What Matters Facebook page , Boston-resident J. Morton has described the grim prognosis given during the early stages of her pregnancy.

"“I went in for an ultrasound and what we thought was going to be a day filled with happy tears and laughter, that day did not turn out as planned,” the post begins.

After the ultrasound revealed Ms Morton’s unborn child suffered a unique defect of the heart, she was advised to expect a stillbirth.

Ms Morton said she refused to accept the possibility her child might die, going on instead to organise a reveal party, a baby shower and a nursery.

Despite suffering heart failure and a heart rate of 40 to 50 beats per minute, Ms Morton’s daughter Clara Ray managed to survive to 37 weeks and was delivered via C-section on June 14 of this year.

Clara received heart surgery on her sixth day as well as receiving a few more diagnoses. Four months on, she continues to defy the odds.

Ms Morton has described watching Clara’s recent reaction to seeing her first snowfall, saying it left her with a feeling of profound happiness.

"I can't explain the emotions we felt, as we watched that smile come across her face,” Ms Morton wrote.