Genetic Prenatal Testing of the Second Trimester

During the second trimester, genetic prenatal testing will be recommended by your health care practitioner. Are there any risks from prenatal tests?

...risks to you?

...risks to your baby?

The answer is yes on both counts but the risks are mostly to your unborn baby.

Also know that you have the right to refuse any test.

Prenatal tests of the second trimester:

Amniocentesis

Maternal Serum Alpha-Fetoprotein

Cordocentesis

Integrated Screen

Genetic Ultrasound

Second Trimester Genetic Prenatal Testing:
Amniocentesis

Amniocentesis is a genetic prenatal testing performed between 14 and 20 weeks of pregnancy although some facilities perform amniocentesis it as early as 11 weeks.

An ultrasound is used as a guide to determine a safe location for the needle to enter the amniotic sac so some of your baby's amniotic fluid can be safely removed.

In this manner a sample of amniotic fluid is collected through the needle.

The procedure of this genetic prenatal testing takes about 45 minutes, although the collection of fluid takes less than five minutes.

Results can take anywhere from a few days to a couple weeks to be returned.

Amniocentesis can be used later in the third trimester for a few reasons:

Prenatal paternal tests

Another reason would be if your bag of water - also referred to as membranes - rupture prematurely (PROM). In this case an amniocentesis would be performed to assess any risk of infection to your baby.

An amniocentesis may also help determine the severity of fetal anemia in babies with Rh disease. This would assist your care provider in determining whether your baby requires a blood transfusion.

It is sometimes done to assess the lung maturity of a baby. In this case, it is done shortly before delivery.

Amniocentesis is used to detect chromosome abnormalities, neural tube defects and genetic disorders. The most common neural tube defect being spina bifida.

It is 98 to 99% effective.

It is recognized as an

invasive genetic prenatal testing

Miscarriages can also occur because of an infection in the uterus (due to the needle), the water breaks (again due to the needle) or labor is induced prematurely (due the trauma of the procedure).

Although extremely rare, it is possible for the needle to come in contact with your baby. Great precautions are taken that this does not occur by using an ultrasound to guide the needle away from your baby.

You - the mother - may experience a sharp pain when the needle enters the skin and again when it enters the uterus.

Cramping

Leakage of fluid

Minor irritation around the puncture site

Bruising

Note: this happened to my sister-in-law which left a huge bruise on her tummy. She required 4 days of total bed rest.

Second Trimester Genetic Prenatal Testing:
Maternal Serum Alpha-Fetoprotein

Maternal Serum Alpha-Fetoprotein Test also known as AFP and MSAFP

MSAFP is not a genetic prenatal testing. It examines the level of alpha-fetoprotein in your blood during pregnancy. It is not a diagnostic test. Screening tests do not look only at results from the blood test.

They compare a number of different factors - including age, ethnicity, results from blood tests, etc - and then estimate what your chances are of having a baby with an abnormality.

These tests DO NOT diagnose a problem, they can only signal that further tests should be done.

Blood is drawn from your veins and then sent off to a laboratory for analysis. The results are usually returned between one to two weeks.

MSAFP is performed between the 14th and 22nd weeks of pregnancy. However it seems to be most accurate during the 16th to 18th week.

Your levels of AFP vary during pregnancy so accurate pregnancy dating is imperative for more reliable test results. High levels of AFP may suggest that your developing baby has a neural tube defect such as spina bifida or anencephaly. However, the most common reason for elevated AFP levels is inaccurate dating of the pregnancy.

Abnormal levels may also be a result of the following:

A multiple pregnancy

Pregnancies that are more or less advanced than thought

There are approximately 25 to 50 abnormal test results for every 1,000 pregnancies tested. Of these results only 1 in 16 to 1 in 33 will actually have a baby that has been affected with a neural tube defect or another condition.

Abnormal test results will warrant an additional prenatal genetic testing in order to make a diagnosis.

A more conservative approach involves performing a second MSAFP followed by a high definition ultrasound. If the testing still maintains abnormal results, a more invasive procedure such as amniocentesis may be performed. Except for the discomfort of drawing blood, there are no risks or side effects associated with the MSAFP.

Second Trimester Genetic Prenatal Testing:
Cordocentesis

Cordocentesis, also sometimes called Percutaneous Umbilical Cord Blood Sampling (PUBS), is a genetic prenatal blood test that examines blood from the baby to detect fetal abnormalities.

An ultrasound determines the location where your baby's umbilical cord inserts into the placenta. The ultrasound guides a thin needle through your abdomen and uterine walls to the umbilical cord.

The needle is inserted into the umbilical cord to retrieve a small sample of fetal blood. The sample is sent to the laboratory for analysis, and results are usually available within 72 hours.

The procedure is similar to amniocentesis except that the objective is to retrieve blood from the baby rather than amniotic fluid. Cordocentesis is usually done when diagnostic information cannot be obtained through amniocentesis, CVS, ultrasound or if the results of one of these prenatal genetic testing was inconclusive.

It is performed after 17 weeks of pregnancy.

Pregnancy loss is the primary risk related to cordocentesis occurring between 1 to 2 times out of every 100 procedures. Other potential side effects include:

Blood loss from the puncture site

Infection

Drop in fetal heart rate

Premature rupture of membranes - PROM

Fever

Chills

Leaking of amniotic fluid

Second Trimester Genetic Prenatal Testing:
Integrated Screen

An integrated prenatal screen combines the use of other prenatal genetic screens:

This genetic prenatal testing will detect up to 92% of babies affected with Down Syndrome and up to 90% with Trisomy 18. It will also detect up to 80% of babies that have open neural tube defects such as Spina Bifida.

The results of this test will not be available to you until your second trimester.

So what does it mean for you if you have a positive screen test? Of the women taking the test about 5% of them will have a positive. This means that they have an increase in risk that their baby will have a chromosome anomaly or a neural tube defect not that their baby actually has one such anomally. This mean that further testing will be required: an ultrasound or an amniocentesis.

Integrated Screen is not a diagnostic test. It cannot tell you whether your unborn baby has or doesn't have a problem. It will simply tell you the chances that your baby might have a problem.

Second Trimester Genetic Tests:
: Genetic Ultrasound

A genetic ultrasound is an ultrasound in which physical features of your baby are closely examined to detect whether there is an increased risk for Down syndrome or other chromosomal abnormalities.

To read about the safety of ultrasounds Cick here.

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Sources for Genetic Prenatal Testing:
Mayo Clinic Complete Book of Pregnancy and Baby's First Year. Johnson, Robert V., M.D., et al, Ch. 11.
http://www.americanpregnancy.org/prenataltesting/amniocentesis.html
Williams Obstetrics Twenty-Second Ed. Cunningham, F. Gary, et al, Ch. 13.
http://depts.washington.edu/pdcweb/tests/IntegratedPrenatalScreening.htm

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