How much harm can amnio cause the fetus?

Amniocentesis: An amniocentesis has a small chance of causing a pregnancy loss. That loss is dependent upon the gestational age when the procedure is done. At 16-20 weeks that risk is about 1 in 1600 procedures. As the pregnancy progresses that risk goes way down. In the third trimester an amniocentesis won't cause the pregnancy to be lost, but the baby might need to be delivered.