Second Trimester Tests During Pregnancy
Amniocentesis: This optional test is usually performed between 15 and 18 weeks of pregnancy (but can be done earlier) for women who are 35 or older, have a higher-than-usual risk of genetic disorders, or whose MSAFP or multiple marker test results were suspicious. The procedure is done by inserting a needle through the abdomen into the amniotic sac and withdrawing fluid that contains fetal cells. Analysis can detect neural tube defects and genetic disorders. The miscarriage rate after amniocentesis varies depending on the experience of the doctor performing the procedure, averaging about 0.2% to 0.5% at 15 weeks, but the test can detect 99% of neural tube defects and almost 100% of certain genetic abnormalities.
Cordocentesis: This test, also known as fetal blood sampling (FBS) or percutaneous umbilical cord sampling, collects fetal blood directly from the umbilical cord or fetus. This test can be used to measure anemia and blood oxygen levels and to screen for maternal Rh antibodies. Cordocentesis can be done as early as the 17th week of pregnancy.
Fetal Doppler ultrasound: A Doppler ultrasound test uses sound waves to evaluate blood as it flows through a blood vessel. Fetal Doppler ultrasound can determine if blood flow to the placenta and fetus is normal.
Fetoscopy: Fetoscopy allows a doctor to see the fetus through a thin, flexible instrument called a fetoscope. Fetoscopy can detect some diseases or defects that cannot be found by other tests, such as amniocentesis, ultrasound, or chorionic villus sampling. Because fetoscopy carries significant risks for the mother and fetus, it is an uncommon procedure that is only recommended if there is a much higher-than-normal chance that the baby will have an abnormality.