• Ultrasound (or sonography) is a procedure that can be performed from the fifth week of pregnancy up until delivery, but it is generally done after the sixteenth week. The test uses sound waves to produce a picture of the fetus (sonogram) without the danger of x-rays. Most ultrasound machines have a TV-like screen that provides parents-to-be a unique opportunity to see their baby. Often they can even get a copy of the sonogram to show to family, friends and their child in later years.  If performed early, ultrasound it can be used to date a pregnancy. Later, it can be used to identify possible causes of a problem such as vaginal bleeding, determine the condition of the placenta, diagnose a multiple pregnancy, determine whether the baby is growing properly and verify breech presentation or another uncommon fetal or cord position prior to delivery.  Although in 25 years of clinical use and study, no harmful effects have been associated with ultrasound, the American College of Obstetricians and Gynecologists (ACOG) still recommends the procedure be performed only when necessary - not on a routine screening basis. Many obstetricians provide Ultrasound services in their offices.

• Alpha-Fetoprotein (AFP) Screening, performed between the fifteenth and eighteenth week of pregnancy, analyzes the mother's blood to detect the possibility of abnormalities in the baby's brain or spinal cord or a chromosomal disorder such as Down's syndrome. The problem with the AFP test is the high number of false positives it produces. If you have an AFP screen, remember, it is only a screening test. Any abnormal results require further testing to confirm a problem. Because the test can detect possibly serious illnesses and poses no danger to the mother or the fetus, experts recommend AFP screening for all pregnant women.

• Amniocentesis, usually performed between the fourteenth and eighteenth week of pregnancy, is a diagnostic test that can identify a number of fetal problems, including Down's syndrome and the possibility of Tay-Sachs disease or sickle-cell anemia. Since Down's syndrome is more common in babies born to older women, amniocentesis is usually recommended for all women over age 35.

  Here is how an Amniocentesis works: 
  The doctor inserts a slender needle through the abdomen and into the amniotic sac and extracts fluid for examination. Through chromosome analysis the test can also reveal the sex of the fetus.

• Chorionic villus sampling (CVS)–detects genetic disorders.