The offering of amniocentesis or chorionic villus sampling (CVS) for chromosome studies is recommended for pregnant women at high risk for Down syndrome. The offering of screening for Down syndrome by serum multiple-marker testing is recommended for all low-risk pregnant women, and as an alternative to amniocentesis and CVS for high-risk women (see Clinical Intervention). This testing should be offered only to women who are seen for prenatal care in locations that have adequate counseling and follow-up services. There is currently insufficient evidence to recommend for or against screening for Down syndrome by individual serum marker testing or ultrasound examination, but recommendations against such screening may be made on other grounds (see Clinical Intervention).