If you do not pass the Down’s syndrome screening test, other tests may be done to determine if the fetus is at risk for Down’s syndrome. Down’s syndrome screening is done between 15 and 21 weeks of pregnancy and involves drawing blood to check several values to determine if the fetus is at risk for Down’s syndrome. If the result is a critical or high risk, the risk of Down’s syndrome is usually considered high and further testing is recommended, either non-invasive genetic testing or amniocentesis prenatal diagnosis. Non-invasive genetic testing is also a screening tool and is not a definitive diagnosis. For a definitive result, amniocentesis can be performed, which looks at the 23 pairs of chromosomes in the fetus for abnormalities to determine fetal chromosomal problems.