Emerging technologies over the last 25 years have afforded us the possibility of being able to screen pregnancies for a variety of conditions. Prior to the emergence of screening, complicated pregnancies were often undiscovered until full term. The goal of all prenatal screening is to provide the expecting mother with as much information as possible, in an effort to optimize pregnancy outcomes. An unfortunate side effect of this type of screening is anxiety. It is very important to remember that almost all pregnancies are healthy ones.

There is a small minority of pregnancies in which there are problems with the egg prior to fertilization, or problems with the developing embryo or placenta. These screening of these pregnancies are the focus of prenatal testing. Some of the problems which may be detected include:

• Genetic Disorders
• Spinal Cord Defects
• Placental disorders
• Defects of Anatomy

Genetic Disorders
The most common genetic disorders are not those of single genes (ex. Muscular dystrophy, Tay-Sachs disease, Cystic fibrosis) but rather imbalances of the major pieces of material which hold genes, known as chromosomes. Chromosome imbalances in the egg (collectively called aneuploidy), result in an embryo with an extra chromosome. This condition is called Trisomy, and the most common is Trisomy 21, or Down syndrome, named after John Langdon Down, who first described the range of impact in the 1890’s. Also, Trisomy 13, and Trisomy 18 are observed, and all three increase with advancing age of the mother. Trisomy 13 and 18 are not viable with life, but can live until term pregnancy, and beyond for a short while. Trisomy 21 infants are born with a variable impact on the brain, heart, kidneys, spine, and stomach. There is a very wide range of impact, from very mild, to very severe.

Aneuploidy screening has changed over the past 15 years. In general, the medical world formerly recommended definitive testing with either amniocentesis or chorionic villous sampling (CVS) if the mother was over age 35. This is the age at which the risk of aneuploidy equals the risk of miscarriage due to the amnio or CVS.

However, age alone is insufficient as a screen. Other screening tools include Triple marker screening, integrated pregnancy screening, and the earliest testing, known as First Trimester Screening or FTS.

Spinal Cord Defects
Spinal cord defects are rare in the general population (1:1000). However, the testing is relatively simple: a blood test at 16-18weeks called MSAFP, and a detailed ultrasound at 18-20 weeks to look at the fetal spine and brain. This is considered a standard of prenatal care. It is part of the triple marker screen.

Placental Disorders
There is growing evidence over the last several years that placental function is the cause of severe fetal-maternal complications such as growth restriction, and severe hypertension in pregnancy. One non-genetic spin off from first trimester screening is the reporting of PAPP-A, a protein made from the placenta. In placental disorders, the PAPP-A is in low amounts in the maternal blood system, and this may be a marker for problems in later pregnancy. It is a way to be able to screen for such problems.

Defects of Anatomy
Anatomic defects are generally non-genetic in origin. Problems such heart defects, spinal defects, and facial defects are best seen at the anatomic ultrasound at 18-20 weeks of pregnancy. In the first trimester, we look at all possible anatomy that is visible, to determine problems early if they are present.