When will my doctor do an amniocentesis?

It depends: If the amniocentesis is for genetic screening, it is usually done at 14-15 weeks. If it is for fetal lung maturity, it may depend on the indication, but usually 36 weeks.

16-18 weeks: Amniocentesis is generally done only on women who are at increased risk for a genetic problem like down's syndrome, based on age, family history or other genetic testing. Genetic amnios are done around 16-18 weeks and carry about a 1in 300 chance of miscarriage related to the procedure. Amnios are sometimes done later for infection or testing to see if it would be ok to deliver the baby early.

16 weeks: Typically they are done at 16 weeks.

Time Amniocentesis: The amniocentesis is usually performed at 16 weeks from the last menstrual period. A small portion of amniotic fluid and cells are removed. Analysis will give a chromosome picture of your baby, and will detect chromosome abnormalities.

If YOU approve: Amniocentesis is an invasive procedure. There are risks. Getting certain information is the benefit. In all cases a pregnant woman should be told the risks and benefits for her and her baby. She should be able to ask the doctor how many procedures he/she has done in cases like hers (gestational age, amount of fluid, baby and placenta position, etc). Only then should she decide whether to proceed.