1. Prior to formal amniocentesis, the physician performs an ultrasound examination to determine fetal size, gestational age, fetal position, and number of fetuses;
2. Under ultrasound guidance, identify the optimal insertion site;
3. Disinfect the mother's skin;
4. Place a sterile drape over the mother's abdomen;
5. Under ultrasound guidance, gradually insert a 20- or 22-gauge spinal needle into the previously selected amniotic cavity;
6. Once the needle is confirmed within the amniotic cavity, begin aspirating amniotic fluid using negative pressure;
7. Discard the first 2 milliliters of fluid (to prevent maternal cell contamination);
8. Extract approximately 20 milliliters of amniotic fluid;
9. Replace the inner cannula of the needle;
10. Withdraw the entire needle;
11. Apply a bandage to the puncture site on the expectant mother's abdomen. She should rest for 10 minutes outside the amniocentesis room. If no discomfort occurs, she may return home to await results.