Screening for Birth Defects
Birth defects occur in up to 3-5% of pregnancies with a wide range of severity and outcomes.
Different types of birth defects:
- Chromosomal – Chromosomes can be abnormal number, missing or extra pieces of chromosomes.
- Trisomy – extra chromosome (Trisomy 21 is commonly called Down syndrome).
- Monosomy (missing chromosome), deletions and duplications of parts of chromosomes).
- Inherited genetic disorders- muscular dystrophy, cystic fibrosis, or sickle cell disease, others
- Structural birth defects- cleft lip, club foot, neural tube defects, cardiac defects, other
Diagnostic Vs. Screening Tests
Diagnostic Tests: Amniocentesis, Chorionic Villus Sampling
- Usually used for patients with risk factors (age, prior pregnancy, family history, abnormal screening test)
- Definitive results (yes or no)
- Invasive – Risk of leakage of amniotic fluid, infection, bleeding and miscarriage.
- Usually for low risk pregnancies, but may also be used with advanced maternal age if patient desires screening only
- Result not definitive (Not yes or no result, but a calculation of risk, which if increased may lead to further testing.)
- Non-invasive- no risk
- Blood from parents can be tested to see if they carry a genetic condition that could be passed on to the baby. This can be done anytime during or before pregnancy.
- Cystic fibrosis- All patients regardless of ethnic or family history should consider screening.
- Other genetic disorders- Testing should be considered based upon personal or family history or ethnic background
Deciding to screen for birth defects
Who should screen for birth defects:
- Patients at increased risk or who want definitive results should consider referral for genetic counseling and diagnostic testing
- Any positive or abnormal result should be followed up with genetic counseling and consideration of further testing.
- May be helpful to know in advance the health of the baby for planning and possibly improved care before and after birth
- Decision should be made by the parents based upon information about the available tests.