Genetics Northern California

Prenatal Services

Prenatal testing helps find some genetic conditions and birth defects during pregnancy.

Most babies are healthy, but about 1 in 30 (3%) will be born with a condition that may need medical attention. These conditions can range from mild to severe. They can affect physical and mental development. Usually, there is no history of these conditions in the family.

You can decide if you want testing that looks for certain types of conditions. You can also decide not to have testing.


What Prenatal Tests Can Find

Prenatal tests can help find some conditions, but no test finds everything. Here’s what testing can look for during pregnancy:

Common chromosome conditions (like Down syndrome and trisomy 18)

·       Do not usually run in families

·       Can happen randomly in any pregnancy

·       The chance increases with age

o   From 1 in 525 (at age 20) to 1 in 20 (at age 45)

o   See the maternal age chart for the chance at all ages

Rare chromosome conditions (such as 22q11 deletion syndrome)

·       Often happen randomly, but can be inherited

·       Found in about 1 out of every 200 pregnancies

·       Not related to a person’s age

Rare recessive conditions (like spinal muscular atrophy, cystic fibrosis, and sickle cell disease)

·       Anyone can be a healthy carrier for a recessive condition

·       About 1 in every 80 pregnancies is found to be at-risk

·       There is usually no history of the condition in the family

·       Not related to a person’s age

Physical differences (like spina bifida, abdominal wall defects, and heart defects)

·       Usually happen randomly

·       Found in about 1 out of every 100 pregnancies

·       Not related to a person’s age

Types of Prenatal Testing

Prenatal testing includes screening tests and diagnostic tests.

Screening tests estimate the chance for certain conditions. Screening can tell if a baby has a higher or lower chance for the conditions being tested. More testing is needed to be sure. 

Diagnostic tests can tell you for sure about certain conditions during pregnancy.

Optional Tests During Pregnancy

The following tests are routinely offered during pregnancy. These are all optional.  The decision to have any of these tests is up to you.  

Cell-free DNA (cfDNA) screening - also called NIPT
Screens the pregnancy for common chromosome conditions, such as Down syndrome (trisomy 21), trisomy 18,  and trisomy 13. More testing is needed to make a diagnosis.

Maternal serum alpha fetoprotein (MSAFP) screening
Screens the pregnancy for open physical birth defects (like spina bifida and abdominal wall defects). More testing is needed to make a diagnosis.

Diagnostic testing (CVS or amniocentesis)
Accurately diagnoses chromosome conditions in a developing baby. May also help diagnose some physical birth defects (like spina bifida). Microarray testing can be requested to diagnose rare chromosome conditions. Extra testing may be included when a baby is at risk for an inherited condition.  

Genetic carrier screening
Finds healthy carriers of rare, recessive conditions. Both biological parents may need testing to know if a pregnancy is at risk. More testing is needed to diagnose these conditions in a baby.

Helps find physical differences in a developing baby (like spina bifida or heart defects). May identify some pregnancies at high risk for chromosome conditions. More testing may be needed to make a diagnosis.

Last Reviewed: September 21, 2022
Reviewed by: Kimberly Barr, MS, LCGC
                       Kaiser Permanente NCAL Regional Genetics