Amniocentesis—Sometimes called an "amnio", is usually given to mothers between 15--20 weeks to women 35+, or to those with a family history of birth defects, as well as those with abnormal results in other prenatal tests.
This minor surgical diagnostic test allows the doctor to obtain a sample of the amniotic fluid. The amniotic fluid is then analyzed to look for genetic characteristics of the baby or to check on the maturity of the baby’s lungs. The amniocentesis is a common way to obtain material for genetic and other testing of the baby. The doctor inserts a long, thin, hollow needle through the mother's abdomen into the uterus and amniotic fluid. Usually the doctor uses ultrasound imaging to guide the needle. The small amount of fluid removed should not affect the baby. The risk of complications from the procedure is low, but, as with any procedure, complications can occur. Be sure to consult with your doctor before the procedure is performed.
Amniocentesis helps the doctor estimate the baby's lung maturity. Because babies often "breathe" amniotic fluid in and out of their lungs inside the womb, the amniotic fluid is chemically similar to the fluid within their lungs. As their lungs mature, the chemical composition changes. These changes can be measured from the amniotic fluid and used to estimate the maturity of the lungs.