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|What Are Prenatal Tests?
They are tests which are carried out on pregnant women to check that their pregnancy is developing normally. There are many different types of tests which can offer information on a variety of development areas. For example, genetic testing can indicate if the fetus is likely to have a genetic disorder. Certain types of ultrasounds can pick up birth defects such as heart disorders. Other tests are used to monitor the baby's size and can provide the gender of the baby. In most instances a woman will be recommended routine prenatal tests and only offered non-routine tests if a potential issue is highlighted or if the mother has a condition which puts her at risk (such as diabetes or heart disease in pregnancy).
A prenatal blood test is routinely carried out by your healthcare provider or OB/GYN during your first prenatal examination (see prenatal visits). Although the blood test may be used to confirm your pregnancy, the results will also be used to check for other potential pregnancy complications. A small sample of blood will be taken from your arm and sent to a lab for analysis. There is no risk to you or your baby with these tests. Blood tests can be used to check the likelihood of a baby having diseases such as Down syndrome. Most initial blood tests are screening only - and this is an important point. Screen tests can only indicate the possibility of a problem. In the case where a blood test indicates a potential problem, other prenatal diagnostic tests (usually more invasive) need to be carried out to achieve more accurate results.
Blood tests carried out in the first prenatal exam check for:
HCG Levels: HCG is the pregnancy hormone. The level of hormone can give an indication as to estimated pregnancy due date. For example levels 5 to 50 indicate the pregnancy is 3 weeks old; 5 to 426 indicates 4 weeks old; 19 to 7,340 indicates 5 weeks old; 1,080 to 56,500 indicates 6 weeks old; 7,650 to 229,000 indicates 7-8 weeks old and 25,700 to 288,000 indicates 9 to 12 weeks old.
Rh Status: Reveals if you are Rh negative or positive and if there is a Rh incompatibility between mom and baby. Problems can arise when the fetus's blood has the Rh factor and the mother's blood does not. These problems can be prevented with early treatment.
Glucose Levels: Taken to screen for gestational diabetes by measuring the body's ability to metabolize sugar. If your glucose level is between 130 to 140 milligrams per deciliter of blood, then your OB/GYN will request a glucose tolerance test. With this test, you drink a special sugary drink from your doctor and a blood sample is taken one hour later to look for high blood sugar levels.
Iron Levels: This is to test your susceptibility to anemia. If the iron levels are low in your blood, your doctor may prescribe supplements or iron injections. Your hemoglobin levels will also be checked – correct levels are between 12-14 grams, and below 10 grams will need treatment.
Toxoplasmosis: Toxoplasmosis is harmless to the mother but it may cross into the placenta and cause harm to the baby. It can cause low birth weight, brain calcification, retinal abnormalities, mental retardation and premature birth.Down Syndrome Risk: HCG and PAPP-A (pregnancy associated plasma protein A) are measured and combined with another measurement called nuchal translucency (nuchal scan) along with the mothers age to give a risk assessment for Down syndrome and Trisomy 18 (Edwards Syndrome). This will not indicate if your baby has Down syndrome, but rather indicates risk. A further more invasive diagnostic test has to be carried out to assess likely presence of either syndrome.
Additionally, a urine test will be taken to test:
Bacteria: Bacteria in the urine can indicate a urinary tract infection. Nearly 10 percent of pregnant women have bacteria in their vaginal area which is dangerous if it spreads to the kidneys. Urinary tract infections are treated with antibiotics that are safe for mother and baby.
Sugar: High levels of sugar in the urine can be one of the symptoms of diabetes.
Protein: Certain levels of blood protein can indicate a urinary tract infection or if pregnant, conditions related to high blood pressure and preeclampsia.
Some tests will be repeated at future prenatal examinations to ensure your pregnancy is progressing normally. Between weeks 16 and 18 you may be offered the quad screen test. The quad screen test is a maternal blood screening test that looks for four specific substances: AFP, HCG, Estriol and Inhibin-A. It is similar to the Triple Screen Test (also know as the Multiple Marker Screening and AFP Plus). However where the Triple Screen tests for AFP, HCG and Estriol - the quad screen additionally tests for Inhibin-A. The quad screen test gives a more accurate assessment of the presence of Down syndrome, Edwards syndrome and other neural defects or chromosome abnormalities such as spina bifida. Any potential issues highlighted by this test may prompt your OB/GYN to suggest further diagnostic tests. At 28 weeks you may undergo a Nonstress test (NST) which highlights any signs of fetal distress due to lack of oxygen. This test is carried out by placing a belt around the mother's abdomen to the monitor the baby. At 36 to 37 weeks, just before childbirth and delivery you are likely to have a Group B streptococcus test. This test looks for bacteria which can cause pneumonia or serious infection in newborn babies. A swab is taken from the rectum or vagina for testing.
Certain tests are considered non-routine and are recommended for women considered in a high-risk pregnancy category. Including:
• Pregnancy after 35. Women in this category are more closely monitored.
Non-routine tests (but still relatively common) include: Chorionic villus sampling test (CVS) and amniocentesis, which commonly test for Down syndrome, cystic fibrosis, familial hypercholesterolemia, sickle-cell anemia, Tay-Sachs disease and thalassemia. Both can also used for a paternity test while pregnant, although most choose to wait until after birth and use a paternity test kit. A third trimester ultrasound scan may be recommended in certain circumstances (such as multiple births or obese patients).
For more on prenatal testing, see the following:
• Paternity Tests - If you were in between relationships, this is a valid test for peace of mind.
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