Genetic Testing During Pregnancy

Why is it important to do genetic testing during pregnancy?

Many genetic abnormalities can be evaluated or diagnosed before your baby is born (prenatally). This depends on the family history and if a known disease-causing mutation has been already identified in the family.

Your obstetrician may recommend that you and your family meet with a geneticist and genetic counselor to arrange for genetic screening tests and/or genetic diagnostic tests during the pregnancy if:

• you or your partner has a family history of genetic disorders
• you have had a prior fetus or baby with a genetic abnormality
• an abnormality may be suspected on a fetal ultrasound.

Genetic counseling is always recommended prior to any prenatal diagnostic testing for genetic disorders. This is also available for couples who have general questions or concerns.

Testing for Genetic Disorders

Many genetic disorders can be diagnosed before birth.

Examples include, but are not limited to, the following:

• Chromosome abnormality
• Down syndrome
• Fragile X syndrome
• Skeletal dysplasia (depending on the type)
• Cystic fibrosis
• More severe forms of osteogenesis imperfecta
• Autosomal recessive polycystic kidney disease
• Spina bifida
• Gastroschisis
• Omphalocele
• And many others.

Types of Genetic Screenings and Diagnostic Testing during Pregnancy

Genetic Blood Test
A genetic blood test is available to women to provide screening for some disorders. Screening tests alone are not diagnostic. If a blood test finds a possible problem, a prenatal diagnostic test may be recommended to confirm a diagnosis. These diagnostic tests include chorionic villus sampling (CVS) or amniocentesis and are used to perform fetal chromosome analysis or microarray analysis of fetal cells.

Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is a diagnostic test usually performed between the 10th to 12th weeks of pregnancy. The perinatologist gently suctions a small piece of the placenta on the outside of the fetal sac to obtain fetal tissue and cells in order to look at fetal chromosomes and/or DNA, and potentially other genetic conditions in the fetus.

Amniocentesis
A genetic amniocentesis is a diagnostic test usually performed between weeks 16 to 20 of a woman’s pregnancy. The perinatologist inserts a hollow needle to remove a small amount of amniotic fluid from around the developing fetus. This fluid has fetal cells floating in it that allow the laboratory to study fetal chromosomes by routine analysis or by microarray, as well as to obtain fetal DNA for other types of genetic testing depending on the family history. This fluid also allows testing for neural tube defects (spina bifida) or abdominal wall defects (gastroschisis, omphalocele) in the developing fetus.

There is another form of amniocentesis that is not genetic, but rather performed when there’s a risk of premature birth, to check if a baby’s lungs have matured; this is not a genetic test.

A Word of Caution About Genetic Testing During Pregnancy

Although advances in genetic testing have improved doctors’ ability to diagnose and treat certain illnesses, there are still some limits. Genetic tests can identify a particular problem in a chromosome or gene, but can’t always predict how severely a person who has the condition will be affected, as all of us are unique. We will do everything we can to help provide the support and information you need, with the understanding that there may be some things we won’t know until your baby is born.

Learn more about prenatal genetic testing at our affiliate laboratory.

Here for You, Before You Need Us

During the course of a pregnancy, prenatal testing may identify issues with your baby that will need attention immediately after birth. You have a choice about where to bring your baby for medical care. At CHOC, our highly trained neonatologists, surgeons, geneticists and other pediatric specialists can meet with your family before birth to discuss a comprehensive plan for your baby and the tests, procedures and treatments he or she will need. Talk to your obstetrician about making CHOC the preferred hospital for your baby after birth.