Amniozentese

Amniozentese, also known as amniocentesis, is a prenatal diagnostic procedure in which a small amount of amniotic fluid is withdrawn from the uterus through the mother’s abdomen under ultrasound guidance. The fluid contains fetal cells and biochemicals that can be analyzed in the laboratory. The test is most commonly performed in the second trimester, typically around 15 to 20 weeks, but it can be done later to assess fetal lung maturity or to investigate certain conditions.

Indications for amniocentesis include advanced maternal age, abnormal results from prenatal screening tests, ultrasound findings suggesting chromosomal or genetic disorders, previous affected pregnancies, or a family history of a genetic condition. It may also be used to test for fetal infections, to determine the fetal sex in cases of sex-linked disorders, or to assess fetal lung maturity in pregnancies at risk for preterm delivery.

Procedure and results: The procedure is usually done on an outpatient basis. After sterilization and local anesthesia, a thin needle is inserted through the abdominal wall into the uterus under continuous ultrasound visualization, and about 20 to 30 milliliters of amniotic fluid is collected. Fetal cells are cultured for chromosomal analysis (karyotype) or analyzed by newer methods such as chromosomal microarray. Additional tests may include targeted genetic testing and measurements of substances such as alpha-fetoprotein or fetal lung maturity markers. Results commonly take about one to two weeks for a karyotype, longer for some genetic tests.

Risks are small but real, including a miscarriage risk of about 0.1 to 0.3 percent, as well as leakage of fluid, cramping, infection, or injury to the uterus or fetus. Alternatives include noninvasive prenatal testing and chorionic villus sampling, depending on gestational age and clinical context.