Screening for chromosomal anomalies: first or second trimester, biochemical or ultrasound?

Prenatal diagnosis pf chromosomal abnormalities can be accurately made by cytogenetic studies of samples obtained from invasive procedures, such as amniocentesis or chorionic villus sampling. Because these procedures are associated with a risk of miscarriage, the common approach is to perform non-invasive test to define an individual woman's risk of having a chromosomal abnormal pregnancy. Screening for chromosomal abnormalities has developed over the last decade. Prenatal screening can be performed in the late first trimester, the early second trimester or in both. Screening test can be carried out biochemically, ultrasonographically or by both modalities. A major goal of screening test is to achieve maximum accuracy and minimum harm at low cost. The integrated test currently meets best those criteria.