Fetal Testing

Fetal Testing

The decision to have fetal genetic testing is a personal one that should be made only by you.  Before you decide on any genetic test, you should decide if the result would affect your pregnancy in any way.  Depending on your personal beliefs and values you may or may not want to proceed with genetic testing.

Some of questions that should be answered before you decide on doing genetic testing are the following:

  • Would knowing about my baby’s genes affect how I manage my pregnancy in any way?  If not, do I really want to have any testing done?
  • Would I want to get information regarding my baby because I want to have choices regarding continuing the pregnancy, giving my baby up for adoption, or just being prepared in case my baby has special needs, or need for immediate extra care at birth.
  • What accuracy am I looking for?  Do I want a diagnostic test that is close to 100% accurate knowing it has a small risk of miscarriage, or do I want a screening test with less than 100% accuracy but no risk of miscarriage?

Remember no test is perfect and absolute.  There is a certain degree of false positive and false negative associated with every test.

Please be aware that these tests are OPTIONAL and our office cannot pre certify OPTIONAL testing.  You should check your insurance coverage before proceeding with these tests as they can be expensive, and some insurance carriers do not cover the cost of them.

Screening tests

FIRST TRIMESTER FETAL TESTING:

Nuchal translucency (NT)

When:  between 11 and 13 6/7 weeks of pregnancy

How:  ultrasound and blood test.

This is a special ultrasound done to measure the fluid filled space in the back of baby’s neck combined with blood test.  This combined with blood test (free Beta hCG and PAPP-A) can detect the risk of carrying a baby with chromosomal abnormalities including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Turner syndrome (monosomy X).  Abnormal NT can also indicate congenital heart malformation.  Detection rate is 90-95% with false positive rate of 2-5%. This test can be done in women pregnant with twins or triplets.

Cell free DNA (Innatal)

When: Done after 10 weeks of pregnancy.

How: it is a blood test.

This test analyzes the DNA from the pregnancy that crosses over into mother’s blood.  This test can not detect all disorders and birth defects or health conditions, but it can detect some of the most common chromosomal abnormalities.  The most common chromosomal problem is Down Syndrome (trisomy 21).  Detection rate for Down syndrome is 99%.  Others include Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Turner syndrome (monosomy X), and Klinefelter syndrome (XXY).  It is not recommended for women with twins or triplets. This test does not check for neural tube defects (opening in the spinal cord). However, it can be followed by a blood test called MSAFP in the second trimester to check for neural tube defects.

SECOND TRIMESTER TESTING:

Quad screen (AFP tetra)

When: between 15 to 22 wks (ideal time is 16-18 wks)

How: blood test

This test measures the level of 4 different hormones in the mother’s blood combined with clinical information about the mother such as her age and weight to determine the risk of developing a baby with Down syndrome, trisomy 18, or open neural tube defect.  Down syndrome happens in about 1 in 800 babies.  Detection rate for Down syndrome is 75%to 80% with false positive rate of 5%.  Trisomy 18 occurs in 1 in every 5000 births, these babies typically do not survive the first year of life.  Detection rate for Trisomy 18 is 73%.  Neural tube defects such as spina bifida and anencephaly, when a baby’s spinal canal does not close, happens in about 1 in 1000 babies.  Detection rate for neural tube defects is 80-90%. 

Anatomy ultrasound

When: 18 to 22 wks

It is an ultrasound for a complete survey of baby’s anatomy including heart, abdomen, face, arms and legs, head, as well as checking the placenta and the fluid around the baby.  This is also the exciting time that you can find the gender of your baby if you want to as long as the baby cooperates!  Certain anatomical abnormalities could be a sign of chromosomal problems, however many babies with chromosomal problems might have completely normal anatomy.  Detection rate of ultrasound for Down syndrome is 50-60%.

DIAGNOSITC TESTS

Chorionic villi sampling (CVS)

When: between 10 and 13 weeks of pregnancy

How: Inserting a needle under ultrasound guidance vaginally or abdominally to take a small sample from the placenta and to directly check the number of chromosomes. 

It is an accurate test, however is invasive.  The risk of miscarriage from this procedure is around 1 in 100.  The accuracy is close to 100%. 

Amniocentesis

When: done after 14 weeks of pregnancy

How:  Inserting a thin needle through mom’s abdomen to take a sample of the fluid around the baby.  It is also an accurate but invasive test with the risk of miscarriage around 1 in 200.  The accuracy rate is close to 100%.

Maternal carrier testing

When: any time before or during pregnancy

How: BloodTest

This is a panel that looks at your genes to determine whether you are a carrier of certain genetic disorders.    A blood test for 22 conditions that can be passed from parent to child even if neither parent has the clinical disease or any symptoms.  No test can check for all genetic diseases, but this panel checks for 22 more common ones such as genes for Fragile X syndrome, muscular dystrophy, and cystic fibrosis.  If you are found to be a carrier for a certain genetic disease, then your baby might be affected by that disease if your partner is also a carrier for the same gene.  At that point you will undergo genetic counseling and your partner will be tested for the same gene to identify risks to your baby.

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