Fetal cells in the amniotic fluid are collected with a long, hollow needle inserted through the abdomen and into the uterus. The cells are then cultured (grown) and examined for genetic defects, such as Down syndrome. Amniocentesis is performed as early as week 14 and as late as week 20.
Performed between the eighth and twelfth week of pregnancy, this test detects defects much earlier in a pregnancy than amniocentesis. CVS holds much promise for the future, when it may be possible for some birth defects to be treated in utero. A long, thin catheter is inserted through the vagina into the uterus, where a sample of the chorionic villi (fingerlike projections of the fetal membrane) is snipped or suctioned off. The sample, which shares the genetic makeup of the fetus, is cultured and examined.
This exam uses sound waves to create a moving picture of the fetus. It is used for many reasons, including measuring the baby’s size, verifying the due date, diagnosing multiple births, evaluating the placenta’s condition and determining the cause of abnormal bleeding. Your doctor may perform ultrasound to locate the position of the fetus before amniocentesis or chorionic villi sampling. The exam can be performed anytime after the fifth week of gestation.