Genetic or baby test. Amniocentesis is generally done for 3 different reasons. It is done at 16-18 weeks to test for genetic problems. It may be done in the few weeks before your due date to test for baby lung maturity to see if it is safe for the baby to deliver. It can be done in the middle of pregnancy to test for signs of infection or blood problems in the baby.
Ask your ob. Ask your OB to explain why they want an amniocentesis.