Two healthy babies have been born on the same day, after a new test screened the embryos for life-threatening genetic conditions

Two families are celebrating the births of healthy babies, both conceived after an Australian-first test to avoid passing on potentially killer genes.

After the birth of Sophie to Jonathon and Alex, whose family has a history of breast cancer, the Sydney mother said "the curse really stops here".

Melbourne's Victoria and Mike, new parents to Benjamin, had not wanted to risk passing on a rare hereditary condition discovered after their first son died at four weeks.

Both babies, born on the same day, were conceived using karyomapping, a new pre-implantation test based on the use of DNA fingerprinting to identify defective genes.

The technique, which was introduced to Australia in November last year by Virtus Health, allows only embryos not affected by a specific disorder to be selected for embryo transfer during an IVF cycle.

Single gene disorders that can be detected through testing using karyomapping include Huntington's disease, muscular dystrophy and cystic fibrosis.

Victoria and Mike's first son, who was unable to breathe on his own, had congenital myasthenic syndrome.

"We were unaware of our carrier status for this condition until we lost our son," Victoria said.

"We desperately wanted children but could not risk passing on this hereditary condition and losing another child."

Alex underwent a preventative double mastectomy last year after discovering she had the BRCA 1 breast and ovarian cancer gene.

She also plans to have her ovaries removed, but she and Jonathon wanted to have a family first.

"We are thrilled to have been able to use this genetic testing to create a daughter, Sophie, who will not be affected by this gene," she said.

HOW IT WORKS
* Both parents have a blood test.
* A genetic reference, or DNA fingerprint, is identified for the part of the chromosome known to carry the gene fault.
* The couple use IVF to create embryos.
* A few cells are removed from each embryo, then tested for the DNA fingerprint.
* If the same DNA fingerprint is identified, the embryo carries the gene fault. If not, the embryo is probably free of the genetic disorder and suitable for transfer to the woman.