Testing for Birth Defects

Please read this important information carefully.

Birth defects affect 3-4% of all pregnancies.  Some, but not all, of the possible birth defects can be discovered by blood tests, ultrasound and genetic testing.

The testing that you decide to perform for your pregnancy is an individual choice based on many factors such as your health, your age, your previous pregnancy experiences and your family’s health history.

There are two types of testing for your pregnancy: screening and invasive testing.

Screening tests have no risk to the fetus or the mother. Screening tests include blood tests and ultrasound.  Screening tests can identify a women who is at higher risk than expected of having a baby with a birth defect, but cannot detect all of these birth defects (such as spinal cord defects or heart problems).

Invasive tests have a very small risk to the fetus and an extremely rare risk to the mother.  Invasive tests include chorionic villous testing and amniocentesis.  Invasive tests can diagnose chromosomal birth defects in the fetus (such as Down’s syndrome).

First trimester (11-13 weeks) screening tests includes a blood test combined with an ultrasound (Ultrascreen).  This testing can detect up to 90% of Down’s Syndrome and up to 98% of Trisomy13, Trisomy 18 and Turner’s syndrome.

Second trimester (15-20 weeks) screening tests include a blood test (MSAFP) done at 15 weeks in our office.  This test predicts your risk for spinal cord defects (neural tube defects), Down’s syndrome and Trisomy 18. An AFP test can be done for only spinal cord information or both spinal cord and Down’s syndrome. 

The AFP Quad Screen is a blood test that helps to identify pregnancies that may be at risk for certain types of birth defects or chromosomal abnormalities available to women between 15 and 20 weeks of pregnancy. The AFP Quad screen will detect approximately 85% of open neural tube defects (spina bifida). About 1-2 out of every 1,000 babies are born with a NTD and up to 90% are born to families who have never had a baby with this type of birth defect. The AFP Quad Screen will detect about 85% of open NTD’s. The AFP Quad Screen has also been useful for screening for Down’s Syndrome. Down’s Syndrome is a genetic (chromosome) disorder that occurs in about 1 out of 800 births and is characterized by mental retardation and other serious birth defects. The AFP Quad Screen will detect approximately 75% of all Down’s Syndrome pregnancies.

At 18-20 weeks an ultrasound will confirm your baby’s growth, your due date and can detect 35% of fetal birth defects, but misses 65% of all birth defects.

First trimester invasive testing is called a chorionic villous sampling (CVS).  A small catheter is passed through the cervix under ultrasound guidance to obtain a small sample of the placenta which contains the baby’s chromosomes.  Results take 7-10 days.  This test has a risk of miscarriage of 1 in 200. 

Second trimester invasive testing is called an amniocentesis.  This test is performed by an obstetrician or obstetric radiologist by inserting a needle through the mother’s abdomen into the uterine cavity.  Fluid withdrawn from the uterus contains the baby’s cells and chromosomes.  Results take 7-10 days.  This test has a risk of miscarriage of 1 in 250.

All testing is optional and is your personal choice.

Specially trained genetic counselors can help you decide if invasive testing is right for you.  If you need additional information or referral to any of these counselors or doctors, we can help you.