Melbourne baby a "modern day miracle"

A Melbourne baby is being described as a 'modern medical miracle' after intra-uterine blood transfusions kept her alive for eight weeks before she was born.

Without the transfusions, little Rebecca Bui would not have survived, but now specialists at the Mercy Hospital for Women say she's a tiny marvel.

Baby Rebecca is now a healthy, happy baby, but even before she was conceived, her chances of survival were only 50 per cent.

Mum Heidi has described her baby as a "little miracle".

Early in the pregnancy, Heidi's blood cells developed antibodies that started attacking her unborn baby's positive blood cells.

The first of nine life-saving blood transfusions began at the Mercy Hospital for Women when Heidi was just 18 weeks pregnant.

Fetal medicine specialist Professor Susan Walker said: "It's a miraculous procedure that you can take babies who are so small and while they're still unborn and provide what is life-saving treatment to them."

During the delicate procedure the baby is paralysed so that it doesn't move when the needle is inserted through the mother's stomach into a blood vessel in the umbilical vein.

While the procedure is particularly rare, it's not the first time Heidi needed intra-uterine blood transfusions, her five-year-old son was kept alive with transfusions before he was born.

Alexander received his first blood transfusion when Heidi was just 16 weeks pregnant.

Professor Walker added: "During alexander's pregnancy he required a total of 13 transfusions, it's the earliest we've transfused and it's the most we have given."

Fewer than one in a thousand babies like Alexander and Rebecca will need intra-uterine blood transfusions.