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Harvard Medical School
You should have a serious discussion with your obstetrician regarding whether to have amniocentesis. Amniocentesis may be done anytime between the 14th and 20th weeks of pregnancy to test for fetal abnormalities. To check on fetal lung development, the test may be done late in the third trimester.
Tell your doctor ahead of time if you have ever had an allergic reaction to lidocaine or the numbing medicine used at the dentist's office.
Just before the test, you should empty your bladder.