Test is screening test only , estimate neural tube defect and certain chromosomal abnormalities , it gives information about risk but doesn't allow the definitive diagnosis of any condition , the fact that it's not 100% accurate test means that not all women who have a positive high risk result on quadruple screen will have a fetus with birth defect and test may also be Normal even in presence of birth defect . So fallow your gynacologist opinion and fallow accordingly.