Prenatal Tests: What You Need to Know
During a woman's pregnancy, she wants to make sure that she and her baby are healthy and remain that way until they reach full term. That entails eating healthier and taking prenatal vitamins, getting enough rest, regularly visiting the doctor, and possibly undergoing a variety of prenatal tests. Prenatal tests can detect many problems that may occur during a pregnancy including infections, viruses and birth defects. Done at specific stages of a pregnancy, they provide vital health information so that both mother and baby can receive the best care possible.
Obviously, prenatal tests have their advantages, but some are not always accurate and may carry risks. Some may cause "false positive" results, indicating that the fetus has an abnormality when, in fact, it does not. Others have a slight chance of causing a miscarriage. Some are done routinely and others are optional. That's why it's important to discuss the procedures with your doctor so you are fully aware of the risks involved. If any test shows abnormal results, the American Pregnancy Association (APA) strongly recommends seeking second opinions to rule out possible testing errors. Here is a guide to some of the tests available.
1. Urine Test (urinalysis): Done routinely as part of prenatal care during first prenatal exam and then frequently during subsequent prenatal visits. Used to assess bladder or kidney infections, diabetes, dehydration and preeclampsia by screening for high levels of sugars, proteins, ketones and bacteria.
2. Blood Test: Done routinely as part of prenatal care during first prenatal exam. Used to assess blood type, Rh factor, glucose, iron and hemoglobin levels. Also used to assess immunity to rubella, any sexually transmitted diseases, or a toxoplasmosis infection (a parasitic disease that affects pregnant women). Can also be used to diagnose certain genetic diseases including cystic fibrosis, sickle-cell anemia and Tay-Sachs disease.
3. Ultrasound (sonogram): A non-invasive procedure that uses high-frequency sound waves to scan a woman's abdomen and pelvic cavity, creating a picture (sonogram) of the baby and placenta. It confirms normal fetal development and diagnoses potential problems. Poses no risk to the mother or developing fetus and may be performed at any point during pregnancy. Frequency varies depending on your doctor. Additional ultrasounds will be ordered if an abnormality or pregnancy-related problem is suspected. pregnant women should be offered the AFP Plus test, but it is highly recommended for women who have a family history of birth defects, are 35 years or older, have used possible harmful medications or drugs during pregnancy, have diabetes and use insulin, had a viral infection during pregnancy or have been exposed to high levels of radiation.
4. Chorionic Villus Sampling (CVS): An invasive diagnostic test that detects chromosome abnormalities (i.e. Down syndrome) and other genetic disorders (i.e. cystic fibrosis) with 98 to 99 percent accuracy, but does not measure the severity of these disorders. The procedure involves removing chorionic villi cells from the placenta by using an ultrasound to guide a thin catheter through the cervix to the placenta. Recommended if either partner has a family medical history that reveals potential risks. Usually performed between nine and 12 weeks of pregnancy, one miscarriage can occur out of every 100 procedures performed. The Mayo Clinic reports a one percent chance of getting "false positive" results.
5. AFP Plus (multiple marker screening and triple test): Performed during the 15th and 17th week of pregnancy, AFP Plus is a noninvasive and routine maternal blood screening test (with no risks or side effects) that looks for genetic disorders by identifying the levels of three specific substances:
• AFP (alpha-fetoprotein) - a protein that is normally produced by the fetus
• HCG (human chorionic gonadotropin) - hormone produced within placenta
• Estriol - an estrogen produced by both the fetus and the placenta
This test only notes that a mother is at risk of carrying a baby with a genetic disorder and may have "false positive" results.
6. Amniocentesis: A diagnostic test performed during the 15th and 18th week of pregnancy, or following an abnormal triple test result, to detect chromosome abnormalities (i.e. Down syndrome or Trisomy 21), neural tube defects (i.e. spina bifida) and genetic disorders (i.e. cystic fibrosis) with 98-99 percent accuracy. It does not measure the severity of these disorders and may cause miscarriage even though it's considered a safe procedure. According to the Mayo Clinic, the procedure is performed approximately 200,000 times a year, and the risk of miscarriage ranges from 1 in 400 to 1 in 200, depending on how frequently it is performed at the facility being used.
Amniocentesis may also be used in the third trimester if membranes have ruptured prematurely to assess for uterine infections, to help determine the severity of fetal anemia in babies with Rh disease, and to help a physician determine whether the fetus requires blood transfusions. It may also be done shortly before delivery to assess baby's lung maturity.
Amniocentesis involves collecting a sample of amniotic fluid through a needle that is inserted into the abdomen to the placenta. Although extremely rare, it is possible for the needle to come in contact with the baby. Precautions are taken by using a sonogram to guide the needle away from the baby.
7. Glucose screening: A blood test given between the 24th and 28th week of pregnancy to check for gestational diabetes, a high blood sugar condition that some women get during pregnancy. Pregnant women are most at risk for gestational diabetes if they: have had the disorder during an earlier pregnancy, have previously delivered a very large baby, are over age 35, have high blood pressure or are greatly overweight. Those with parents or siblings who have diabetes are also at risk.
This is not a painful test, but a long one. After drinking a sugary solution, a blood sample is taken an hour later to check the level of sugar in the blood. A positive result doesn't necessarily mean gestational diabetes is present. A second, more definitive exam called a glucose tolerance test (GTT) must be taken to confirm.
Source: American Pregnancy Association.
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