A Gold Coast couple has been granted extra time in court  to sue an ultrasound clinic and doctor after both parties failed to diagnose their unborn daughter with Down syndrome.

A sonographer and a doctor reported that the risk was in the "low range" and advised not to undergo more extensive testing.

The parents claimed they would not have continued with the pregnancy if they had known, and indicated they would seek damages for child-rearing costs of their daughter, who is now four years old.