[amnion + -centesis]
Transabdominal puncture and aspiration of the amniotic sac by ultrasound to remove amniotic fluid. The sample is studied chemically and cytologically to detect genetic and biochemical disorders and maternal-fetal blood incompatibility and, later in the pregnancy, to determine fetal maturity. The procedure also allows for transfusion of the fetus with platelets or blood and instillation of drugs for treating the fetus.
This procedure is usually performed no earlier than at 14 weeks' gestation. It is important that the analysis be done by experts in chemistry, cytogenetics, and cell culture. Cell cultures may require 30 days, and, if the test has to be repeated, the time required may be insufficient to allow corrective action.
The procedure can cause abortion or trauma to the fetus.
The patient's knowledge about the procedure is evaluated, misconceptions corrected, and information provided as necessary. The patient is informed about sensations that she may experience and signs a consent form. The amniocentesis equipment is assembled; amber-colored test tubes are used (or clear test tubes covered with aluminum foil) to shield the fluid from light, which could break down bilirubin. Baseline vital signs and fetal heart rate are obtained, and the fundus is palpated for fetal position and fetal and uterine activity for 30 min before, during, and 30 min after the procedure. The patient is assessed for light-headedness, nausea, and diaphoresis as well as for anxiety, pain, and labor onset. During the procedure, emotional support is provided. After the procedure, the patient is positioned on her left side and is instructed to report unusual fetal hyperactivity or hypoactivity, clear or bloody vaginal drainage, uterine contractions, abdominal pain, or fever and chills, any of which is indicative of complications. Rh-negative women with an Rh-positive fetus should be given RhoGam.
SEE: chorionic villus sampling