Normal results from amniocentesis do not guarantee that your fetus will be healthy.
Amniocentesis can be done to help you prepare if your fetus has a possible birth defect or to help you make a decision about ending the pregnancy if a serious problem is found.
Pregnancy: Should I Have Amniocentesis?
In very rare cases, amniocentesis may be done before 15 weeks of pregnancy. This is rare, because there may be greater risks to your fetus. Talk to your doctor about the risks and benefits of early amniocentesis.
Amniocentesis can't be done easily if the amount of amniotic fluid is very small or if the placenta is in front of your fetus.
Amniocentesis has a very small chance of causing bleeding that could lead to mixing your blood and your fetus's. So if you have Rh-negative blood, you will be given a vaccine (RhoGAM) to prevent Rh sensitization, which could harm your fetus if he or she has Rh-positive blood.
Amniotic fluid has cells that have been shed by your developing fetus. The cells are checked for the number and size of chromosomes (karyotype) to see if there are any problems. For more information, see the topic Karyotype Test.
If you have abnormal results from amniocentesis, you should ask your doctor or a genetic counselor for help in making decisions about the problems your fetus may have and about continuing the pregnancy. It will also be helpful to understand your possible risks with future pregnancies.
Caughey AB, et al. (2006). Chorionic villus sampling compared with amniocentesis and the difference in the rate of pregnancy loss. Obstetrics and Gynecology, 108(3): 612-616.
Seeds JW (2004). Diagnostic mid trimester amniocentesis: How safe? American Journal of Obstetrics and Gynecology, 191: 608-616.
Other Works Consulted
American College of Obstetricians and Gynecologists (2007, reaffirmed 2009). Invasive prenatal testing for aneuploidy. ACOG Practice Bulletin No. 88. Obstetrics and Gynecology, 110(6): 1459-1467.
Wapner RJ, et al. (2009). Prenatal diagnosis of congenital disorders. In RK Creasy et al., eds., Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice, 6th ed., pp. 221-274. Philadelphia: Saunders Elsevier.