What You Need To Know About The 5 Main Antenatal Tests

By in Pregnancy & Labor on 21 January 2009

When you get pregnant, the focus of care by your obstetrician is not only your health but also the health of the baby inside you. Determining any abnormality that you might be suffering from, like medical conditions (e.g. hypertension, asthma, diabetes) can be readily diagnosed because the manifestations are quite obvious. Generally, the diagnostic tests concerning maternal diseases are not that complex and do not usually raise much of a concern.

Unfortunately, this is not the case for your unborn child. Any physical abnormalities your child may be having while still in your womb are imperceptible, unless you subject yourself to undergo a wide variety of tests throughout the nine months before delivery, known as the antenatal testing.

Understand that when you first learned that you are pregnant, your health care provider ordered several blood and urine tests to determine your health status, and not that of your baby. The tests include determining your blood type, checking for anemia, diabetes, proteinuria, making sure you are immune to rubella, and checking for infectious diseases such as hepatits, Chlamydia, HIV or syphilis. Later, the focus of the succeeding tests shifts to checking the well-being of your baby. Medically termed as antenatal tests, they also help determine whether your baby has congenital anomalies or genetic conditions.

1. Ultrasound scan. This is a procedure that uses sound waves that bounce off the developing fetus creating an image which is then projected onto a TV screen. This is done at any time throughout the pregnancy. For example, an early ultrasound scan may be ordered to check the number of fetuses, presence of fetal heartbeat, to rule out ectopic pregnancy and blighted ovum, and to determine the due date. In the middle of the pregnancy, an ultrasound can also determine the fetal gender, and check if the fetus is growing well as expected, as well as the amount of amniotic fluid inside. Closer to the due date, an ultrasound may be ordered by your health care provider to make sure your baby is in a correct position to exit the birth canal.

2. Triple Marker Screen. Best done at 15-20 weeks age of gestation, this is a blood test that determines the levels of the three maternal hormones- alpha-fetoprotein(AFP) , human chorionic gonadotropin (hCG) and estriol. Abnormally high level of AFP raises a strong suspicion of the presence of neural tube defects like spina bifida. Down Syndrome (trisomy 21) is marked by low levels of AFP and estriol and high of hCG level. The sensitivity of this test to trisomy 21 is 60%. Edward Syndrome (trisomy 18), on the other hand, is marked by low levels of all the three hormones.

3. Chorionic Villous Sampling (CVS). This is a test that carries a 0.7% risk for miscarriage. This is because the test involves a very fine needle inserted into your abdomen to obtain a placental tissue sample for testing. CVS is best done at 9-12 weeks age of gestation.

4. Amniocentesis. This test has a 0.5% risk for miscarriage. When the triple marker screening indicates trisomy or chromosomal defects, amniocentesis is done for confirmation. Using ultrasound as a guide, the doctor pierces the amniotic sac to get an amniotic fluid sample for karyotyping to actually establish the presence of a chromosomal defect. Amniocentesis is best done at 15-20 weeks for karyotyping and biochemical studies, at >24 weeks for Rh isoimmunization, and at >34 weeks for determination of fetal lung maturity.

5. Percutaneous Umbilical Blood Sampling (PUBS). Carrying a risk of about 1-2 % for miscarriage, PUBS is done by aspirating fetal blood from the fetal umbilical vein. The blood is sent for karyotyping to determine chromosomal abnormalities. The blood sample can also be used for antibody detection and blood typing of the fetus. PUBS is best performed at >20 weeks age of gestation.

While these antenatal tests provide the best information you can possibly get regarding the well-being of your baby; they are not compulsory especially that some of them carry a small risk for miscarriage. Besides, congenital anomalies are rare; and its diagnostic tests are not practical and sensible to be included in the routine tests for all pregnant women.

Therefore, the decision to submit to such tests is a personal call. If it can put your mind at rest, especially if you are apprehensive of your pregnancy because you might have experienced problems with your previous pregnancies, or there is a family history of a certain condition, then by all means, go ahead.

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