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Prenatal Testing

May 28, 2012

So, we’ve already established that I’m old and got pregnant at 39 and I think we all know the potential risks of getting pregnant after 35. In my previous post Yo Momma’s so old we briefly discussed the advances in medicine that allow for testing to help determine whether or not your baby is likely to have a genetic defect or not.

This was a very, very sensitive, and downright terrifying topic for me. I’ve grown more paranoid and neurotic in my old age and didn’t think twice about getting the tests done (as they are optional).

Every couple has a 3-4% chance of having a baby with a birth defect. The risk may be less or more than this depending on many factors including age, medical conditions, medication use, and family history. Prenatal testing for certain disorders is optional for all couples. There are screening tests and diagnostic tests to give you more information about your specific risk in this pregnancy. Each test has benefits and risks and the options can be confusing. There is no test available that can identify every possible birth defect or medical condition of a baby. There is no guarantee despite any testing done that a condition is diagnosed or that you will have a healthy baby.

Types of conditions tested for:

Neural Tube Defects: this category of birth defects comprises problems with how the brain and/or spinal cord of the fetus formed. These structures develop from the neural tube of the embryo. If this tube does not close appropriately (usually occurs 30 days after conception), this type of defect can occur. These problems range from spina bifida (an opening in the spine and spinal cord causing a range of disabilities) to anencephaly (an absence of the brain). The risk of having this condition is 1/500 and does not change with maternal age.

Chromosomal abnormalities: Chromosomes are structures in every cell that carry genetic information. Normally a person has 23 pairs of chromosomes or 46 total. If a pregnancy gets too many or not enough chromosomes, problems arise. Usually these pregnancies miscarry. If miscarriage does not occur, a baby may be born with mental and physical disabilities, sometimes incompatible with life. One of the most common chromosome abnormalities is Downs Syndrome, or Trisomy 21, which is an extra chromosome 21. In this condition, there are three chromosome 21s instead of two. Another chromosome abnormality that can be sometimes detected with prenatal testing is Trisomy 18, a lethal complication resulting in fetal or neonatal death. The risk of having a baby with a chromosomal abnormality increases with maternal age. However, because younger women have more babies, 80% of all chromosomal abnormalities are found in mothers less than 35 years of age.

Optional Screening Tests:

These tests DO NOT diagnose or prove there is a problem. They simply can change your estimated risk of having a baby with certain disorders but do not give you a “Yes/No” that your baby does or does not have the condition tested for. There are false positive and false negative results with these tests. So, even normal tests do not guarantee the birth of a healthy baby. If you have abnormal results of these tests, one of the diagnostic tests would be offered to give you further information.

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*First trimester screening measures the nuchal translucency (fluid area behind the neck) of the fetus and 2 proteins in maternal blood. All this information is also combined with maternal age to get a risk assessment for Trisomy 21 and Trisomy 18. If you do this test, then instead of the Quad screen at 15-20 weeks we offer an AFP (alpha fetal protein) maternal blood test to screen for neural tube defects.

Optional Diagnotic Tests:

These tests are more accurate at finding a fetal problem but they are looking for specific problems. Even a normal result of one of these tests does not guarantee a healthy baby. The trade off with improved accuracy of these tests is having a risk to the fetus. Some women do these diagnostic tests after abnormal screening test results and some women do diagnostic testing without previous screening tests. These tests are usually performed by a high risk obstetric specialist and we will refer you if you desire one of these tests.

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There are risks and benefits to these tests and it is an individual decision for each family whether to do any of these tests and which ones. You do not need to do any screening or diagnostic testing. The benefits of any prenatal testing include reassurance, or in the event of a problem, preparation, optimal medical management, or termination of the pregnancy. The risks including additional worrying if you have abnormal screening tests but don’t do diagnostic testing and the miscarriage risks associated with diagnostic testing. This risk of not doing any testing is not knowing about a birth defect, or a higher risk of one, before delivery.

Fortunately, my initial tests came back good, so I didn’t have to have an amniocentesis. What I can tell you is, the waiting (between the tests and results) was the hardest part for me and knowing how hard it is to have a healthy child – I give credit to every Mom, Dad and family member that has had to deal with the alternative.

*Information courtesy of Haugen OBGYN


From → During, Pregnancy

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