How is it detected and is it possible to detect on unborn child?

“On a blood test for sickle cell disease on newborns……..If the test shows the presence of sickle hemoglobin, a second blood test is performed to confirm the diagnosis. These tests also tell whether the child carries the sickle cell trait.”

If parents take the blood test they can be able to know if the unborn child will have de disease. 

(American Sickle Cell Anemia Association, 2010)