What is genetic counseling? 
Genetic counseling is an educational process during which the known or potential risks of the pregnancy, capabilities and limitations of genetic screenings, and other testing options are discussed. Genetic counseling involves constructing detailed family, medical, and pregnancy histories to assess possible risk factors. 

What are Down syndrome, trisomy 18, and trisomy 13? 

Down syndrome (also known as trisomy 21), trisomy 18, and trisomy 13 are chromosomal abnormalities involving an extra copy of chromosome #21, chromosome #18, and chromosome #13, respectively. These chromosome abnormalities occur after a chance mistake in cell division. Although such abnormalities can occur in any pregnancy, they happen more often with increasing maternal age. Down syndrome causes characteristic facial appearance, intellectual disability, and a greater tendency for other birth defects and health-related issues. Trisomy 18 and trisomy 13 are more severe abnormalities, usually resulting in multiple birth defects and neonatal death.

What are chromosomes? 
Chromosomes are the inherited structures in the cells of the body. There should be 46 chromosomes in each cell, arranged into 23 pairs. Chromosome abnormalities involving a missing or extra chromosome are not usually inherited and are not caused by an exposure during pregnancy. Instead, they are caused by random events in cell division at the time of conception and can occur in anyone's pregnancy. 

How is non-invasive prenatal screening (NIPS) performed? 

Genetic counseling and ordering of screening studies can be coordinated through the Prenatal Diagnostic Center of The Harvey Institute. Prenatal cell-free DNA screening uses a blood sample to analyze pregnancy derived DNA in maternal circulation. This screening can assess risk for chromosomal abnormalities, including trisomy 21, trisomy 18, trisomy 13, sex chromosome abnormalities, and select microdeletion syndromes.

How accurate is non-invasive prenatal screening? 
Prenatal cell-free DNA screening will identify about 99% of pregnancies with Down syndrome as well as most pregnancies with trisomy 18 or 13. There is a small risk of a false positive or false negative with this test, as well as a small non-reportable rate.

What do positive and negative results mean? 
A positive test result indicates an increased risk for a specific chromosome abnormality. A positive test result is not diagnostic, but instead indicates that an increased risk for a problem exists and that additional testing should be considered. Similarly, a negative result does not rule out these abnormalities, but it decreases the specific risks for chromosome abnormalities in pregnancy.

What is assessed during first trimester ultrasound? 
The staff is certified to perform the nuchal translucency and nasal bone assessment at GBMC, which can modify risk for chromosomal abnormalities and provide early detection of some birth defects. Prenatal cell-free DNA screening is often performed in conjunction with the ultrasound exam and genetic counseling.

Is there a need for additional testing? 
If a positive test result or significant ultrasound finding is obtained, a genetic counselor will explain the results and review options for further testing, which may include CVS or amniocentesis and high-resolution ultrasounds. Maternal serum AFP screening for neural tube defects is recommended at 16 weeks. A detailed ultrasound to screen for neural tube defects and other birth defects is recommended at 18-20 weeks of pregnancy.

What is diagnostic testing? 
Prenatal diagnosis through CVS or amniocentesis is available to detect chromosome abnormalities or test for other specific genetic conditions when appropriate. CVS is typically performed between 10.5-13 weeks gestation, and amniocentesis is typically performed between 16-18 weeks gestation but can be performed later. CVS is used to collect a sample of chorionic villi, which are small pieces of placental tissue. An amniocentesis uses a sample of amniotic fluid which contains cells that have been shed by the fetus. Because these procedures are invasive, there can be small risks for complications such as miscarriage. However, they give the benefit of being able to provide definitive, diagnostic information.