Medical technology has improved over the past several years to the point that pregnancies can be tested for high-risk situations and the fetus can be checked for abnormalities as well as illnesses. There are many different ways to do prenatal testing. In diagnostic testing, a positive result typically means that the child in question does have the condition for which he is being tested. When screening for a disease or question, the doctor is simply trying to estimate the risk of the child having the condition. While diagnostic tests tend to be more expensive and invasive, screening exams are quick and easy to do. Screening tests however, have more of a chance of being wrong or producing a false positive or a false negative. There are four types of screening and diagnostic testing for Down syndrome. These include maternal serum screening, ultrasound screening, amniocentesis, and Chorionic villus sampling.

Maternal serum screening is the process of checking the mother's blood for a combination of specific markers. The first of these markers is alpha-fetoprotein, which is made in the part of the womb, called the yolk sac and is also made in the liver of the fetus. This substance is transferred into the mother's blood and in Down syndrome shows up in lesser amounts than in normal pregnancies. The second marker is estriol, which is a hormone, produced by the placenta, and is also decreased in a Down syndrome pregnancy. The third marker is human Chorionic Gonadotropin, which is also produced by the placenta and is used to test for pregnancy. There is a smaller part of the hormone called beta subunit, which is increased in a Down syndrome pregnancy. These three markers make up the standard tests and are commonly referred to as the "triple test".

When a fourth marker called inhibin A is added the screen is called a "quadruple screen". Inhibin A is a protein secreted by the ovary and is increase in the blood of mothers carrying a Down syndrome fetus. When these markers are screened for and put together with the maternal age, the doctor can calculate the risk of the mother to be carrying a baby with Down syndrome. These screens are typically done between the 15th and 18th week of pregnancy. PAPP-A is another marker than can be tested for earlier in pregnancy. It is a protein that is produced by the covering of the newly fertilized egg. In the first trimester, low levels of this protein in the mother's blood can signify Down syndrome in the fetus.

Ultrasound screening can be used to pick up serious medical problems that can indicate Down syndrome. Most commonly, the fetus is screened for blockage in the small intestine and heart defects. In addition, most doctors will be looking for bowel and kidney changes that can be indicative of Down syndrome. Even the best ultrasound can only be used as a prediction of Down syndrome and not as a diagnosis. To determine an accurate diagnosis a chromosomal test needs to be done.

Amniocentesis is used to collect the amniotic fluid, which is the fluid that surrounds the baby in the womb. The fluid contains fetal cells, which can be tested for chromosomal abnormalities. The results take approximately 2 weeks to come in but can provide a positive diagnosis of Down syndrome. Similarly, in Chorionic villus sampling instead of sampling the fluid, a small amount of tissue is taken from the placenta. These cells also contain the chromosomes that need to be studied to determine and accurate diagnosis of Down syndrome.