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Prenatal Testing

prenatal testsAll pregnant women ask the question, “Is my baby healthy?” We all agonize over whether we’re eating all the right foods, if we’re doing anything that could harm the baby, and we even suffer through many uncomfortable pregnancy symptoms just so we can greet our baby in nine months. Your baby’s health and development is important, since we all want to have healthy, happy babies.

Although most babies are born healthy and normal, there are some babies who may need special care due to genetic disorders, prematurity, and etc. Many health problems can be detected during pregnancy through the help of prenatal testing.

What is Prenatal Testing?

Prenatal testing gives you vital information about your baby’s health and well-being during pregnancy. There are two types of prenatal tests – screening tests and prenatal diagnostic testing.

  • Prenatal screening tests detect risks for possible health problems. Screening tests in pregnancy include routine blood tests and ultrasounds. They aren’t harmful to your unborn baby, but they can detect potential problems – like Down syndrome or another chromosomal defect. Keep in mind that a screening test identify whether or not your baby is more likely to have certain problems or genetic conditions, but they do not make a definite diagnosis. They just tell you your risk for having a bay with a problem.
  • Prenatal diagnostic tests, on the other hand, will give you a definitive answer on whether or not your child does indeed have a genetic or chromosomal problem. If your prenatal screening tests indicate that there may be a problem, or you’re at high risk for having a problem, your OB/GYN or healthcare provider will recommend that you have diagnostic testing. Prenatal diagnostic testing includes chorionic villus sampling (CVS) and amniocentesis. Both of these diagnostic tests carry a small risk of miscarriage. Because of this miscarriage risk, before making the decision to undergo prenatal diagnostic testing, you should weigh the risks and benefits of the test.

Prenatal Screening Tests

Prenatal screening tests include blood tests, urine sampling, and ultrasound.

At each prenatal visit in pregnancy, your OB/GYN, midwife or healthcare provider will ask you for a urine sample to check for any urinary track infections, kidney disease, and any signs of gestational diabetes and preeclampsia – a potentially serious pregnancy complication characterized by high blood pressure and protein in the urine. Your blood pressure will also be measured at every prenatal visit.

Your healthcare provider will also use a handheld device called a Doppler to listen to your baby’s heartbeat. After 20 weeks pregnant, your OB/GYN will also start to measure your abdomen to keep track of your baby’s growth. Your developing baby’s growth and heartbeat are two signs that mean everything is going well.

Throughout your pregnancy, you may be asked to give a blood sample. This is part of routine prenatal screening, and it’s used to help your doctor check for the following:

  • Rh Incompatibility – In the first trimester, you will be asked to give a blood sample to determine your blood type and your Rh status (whether or not you are Rh-positive). An estimated 85 percent of Caucasians, 90 to 95 percent of African-Americans, and 99 percent of Asian Americans are Rh-positive. If you are Rh-negative (you don’t have the Rh factor in your blood), this can cause problems in your pregnancy, especially if your baby is Rh-positive. If you are Rh-negative and your baby is Rh-positive, and your baby’s blood somehow leaks into yours, your immune system can start producing antibodies that attack your baby’s blood. For this reason, women who are Rh-negative will get an injection that helps prevent this from happening.
  • Anemia – Early in the first trimester, you’ll have a hemoglobin blood test, which checks for anemia (low red blood cell count). Anemia makes you feel tired, and it can put you at risk for giving birth early (before 37 weeks). Because red blood cells are required to carry oxygen to your unborn baby, it’s essential for your doctor to diagnose this health problem and treat it to prevent pregnancy complications.
  • Sexually Transmitted Diseases – Another first trimester blood test will check for any sexually transmitted diseases or infections, like the human immunodeficiency virus (HIV), gonorrhea, Chlamydia, syphilis, and hepatitis B. Sexually transmitted disease and infections can cause problems in pregnancy, including miscarriage, ectopic pregnancy, preterm delivery, stillbirth, and birth defects. In addition, STDs and STIs can be passed to your baby during a vaginal birth. Sometimes, these infections can cross the placenta and affect your unborn baby. For this reason, healthcare providers want to know if you have any STDs or STIs so that they can come up with a treatment plan to minimize the risks to your baby.
  • Rubella (German Measles) Immunity – In early pregnancy, your doctor or midwife will ask to draw blood to test for your immunity to the rubella virus (the German measles). In the United States, your chances of getting the German measles are low, since most American children are immunized against the virus. A rubella infection in pregnancy can cause you to miscarriage, go into preterm labor, or give birth to a stillbirth. It can also cause birth defects.
  •  Chicken Pox Immunity – Although we generally think of chicken pox as a harmless illness, it can cause a serious birth defect called congenital varicella syndrome (CVS) if you catch it in pregnancy. CVS can cause babies to have vision problems, malformed limbs, skin scarring, abnormally small head, seizures, and physical and mental disabilities. Your healthcare provider will check for your immunity to the virus that causes chicken pox in the first trimester.

In addition to these routine blood tests, there are special first trimester and second trimester screening tests t hat check for birth defects. These screening tests combine special blood tests, along with an ultrasound exam, to check your baby’s risk for having a birth defect.

  • First Trimester Screen – Between 11 and 14 weeks of pregnancy, your doctor or healthcare provider will recommend that you have a first trimester screen. This is a new, noninvasive screening test that combines a blood test (that checks the levels of the pregnancy hormones, hCG and PAPP-A) with an ultrasound evaluation (nuchal translucency screening –which measures the skin thickness at the back of your baby’s neck) to identify your baby’s risk for chromosomal abnormalities, like Trisomy 18 and Down syndrome.This screening test can be performed as a single combined test, or as part of a multistep screening process. The first trimester screen can detect chromosomal abnormalities in 85 percent of chances; with a false positive rate (your baby is healthy, but the test indicates that your baby may have a problem) of 5 percent.The First Trimester screen is considered the most accurate non-invasive screening test available, according to a research study published in a 2005 issue of the New England Journal of Medicine.
  • Multiple Marker Screening (Second Trimester Screen) – In the second trimester, between 15 and 18 weeks pregnant, your doctor will recommend you undergo a multiple marker screening test (also called a triple or quadruple screen) to check for your baby’s risk for chromosomal abnormalities, as well as neural tube defects. In many cases, this test is combined with your first trimester screen. (The combination of screening tests is called integrated or sequential screening.)

The multiple marker screening test checks the level of three or four substances in your bloodstream, including a substance called alpha-fetoprotein (AFP), which is produced by your growing baby; a hormone called estriol, a hormone made by your baby’s liver and the placenta; the pregnancy hormone, human chorionic gonadotrophin (hCG); and inhibin-A, a hormone made by the placenta.

If the results of any of the above screening tests indicate that your baby may have a birth defect, your healthcare provider will recommend that you have prenatal diagnostic testing – which will diagnose your baby. (“Yes, your baby has this birth defect” or “No, your baby is perfectly healthy.”)

Prenatal Diagnostic Tests

There are three main prenatal diagnostic tests that are performed in the United States. These tests will diagnose your unborn baby with a birth defect. These diagnostic tests include:

  • Chorionic villus sampling (CVS) – This diagnostic test is performed late in the first trimester, and it diagnoses chromosomal abnormalities (like Down syndrome) and other genetic disorders. During a CVS procedure, the doctor will take a sample of cells from the placenta and tests it for genetic problems. This diagnostic procedure comes with a small risk of miscarriage.
  • Amniocentesis – This is a prenatal diagnostic test that is performed in the second trimester. For this test, your doctor will extract a sample of you amniotic fluid to check for chromosomal disorders, neural tube defects, and genetic disorders. There is also a risk of miscarriage with this prenatal test.
  • Cordocentesis – Also called percutaneous umbilical cord blood sampling (PUBS), this is a highly specialized diagnostic test that is only performed when the results of a CVS and amniocentesis were inconclusive. Cordocentesis is only performed after 18 weeks of pregnancy, and it removes blood from the umbilical cord. This diagnostic test diagnoses chromosomal disorders, blood disorders, infections, and causes for restricted growth in the baby. Cordocentesis comes with a risk for miscarriage, bleeding at the site of needle entry, uterine infection, and the temporary slowing of your baby’s heart rate.

Should You Have Prenatal Testing?

The decision to undergo prenatal testing is up to you. It’s important that you make an informed decision before declining any tests, especially since they give you important insight into your unborn baby’s health.

Many pregnant women decide to undergo prenatal testing – both screening and diagnostic testing – because they want to know. Normal results ease their anxiety and give them the reassurance that their baby is healthy. Abnormal results, or getting a diagnosis that their baby has a birth defect, can give them an opportunity to think about the future of the pregnancy (whether or not they want to terminate the pregnancy), or it can give them an opportunity to prepare and get ready for their special needs child.

Sometimes, prenatal testing can detect problems that are treatable in pregnancy.

Prenatal testing isn’t always 100 percent accurate. There are false-negative and false-positive results, and the accuracy of the results varies from test to test. This is another factor that you need to consider.

If you ever have a question about prenatal testing, ask your healthcare provider at your next prenatal appointment and get all the details. Ultimately, the decision to have prenatal testing is up to you.

About the author: DP Nguyen is founder and editor of Hip Chick’s Guide to PMS, Pregnancy and Babies. She’s an expert pregnancy and women’s health blogger. She is NOT a medical doctor and does NOT offer medical advice. Connect with her on Google+, Twitter and Facebook.

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