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A Primer to Prenatal Testing
Routine and elective tests can tell a lot about your baby
By Cynthia Booth, M.D.
Preparing for a new baby is a busy and exciting time: choosing a name, decorating the nursery, and celebrating with family and friends. However, the most important job of a mother-to-be is staying healthy, for herself and her baby.
During pregnancy, a prospective mother will see her doctor regularly – at least monthly – and more frequently, as her due date approaches. An obstetrician monitors the mother’s health, as well as the growth and health of the baby, and provides guidelines to follow to provide an optimal environment for baby’s development.
Expectant mothers also have a variety of screening tests available to make sure that their baby is thriving and healthy. Routine tests administered to all pregnant women include blood and urine tests, and blood pressure checks, as well as measurements of the baby’s growth and fetal heart beat measurement. These tests not only monitor the health of the mother and baby, but also give the obstetrician information about the baby: his or her size, sex (if chosen to find out in advance), gestational age, and placement in the uterus.
It’s important to remember that some tests are screening tests, that is, they detect the risk of a potential health condition. Others are diagnostic, which means they can determine – with a good degree of accuracy – the existence of a health condition in the mother or baby. Some of these tests are performed just once, early in pregnancy; some at every obstetrics or OB appointment – weight, urine test, blood measurements and monitoring the baby’s heartbeat – and others, periodically.
Routine prenatal screenings include:
• Blood test – A blood test is given at the first OB visit and sometimes later in the pregnancy. It checks for anemia, or low red blood cell count, which can make mothers-to-be feel especially tired and also raise the risk of pre-term delivery. Blood tests also confirm the mother’s blood type – if it’s not already known – and detects whether the mother has an absence of Rh factor protein that may indicate incompatibility between the mother’s and baby’s blood type. Blood type incompatibility can cause potential health risks for the baby if not recognized and treated. Blood tests will also be ordered. Blood tests will also be ordered that check for various diseases and conditions that may effect the baby’s health such as diabetes, syphilis, hepatitis B and AIDS.
• Urine test – A urine test checks for bacteria in the urine, which could indicate a urinary tract infection; the presence of sugar, a possible sign of gestational diabetes; or protein in the urine, which indicates either an infection or preeclampsia, a pregnancy-related condition that also exhibits high blood pressure and fluid retention.
• Cervical test (Pap smear) – This test is usually performed at the first prenatal visit and checks the mother for cancer of the cervix and certain sexually transmitted diseases, such as Chlamydia, gonorrhea and herpes.
• Ultrasound – An ultrasound is usually first performed at 18 to 20 weeks – although it may be done at the first visit to determine the age of the baby – and sometimes repeated, depending on the nature of the pregnancy and doctor’s recommendations. An ultrasound exam uses sound waves to transmit a picture of the baby. The ultrasound shows the shape and position of the baby in the uterus and the baby’s gender, records the baby’s heartbeat, and looks for physical problems or issues such as cleft palates, congenital heart defects or malformation of internal organs. It also shows the baby’s relationship to the placenta.
• Glucose screening (offered at 24 to 28 weeks) – This blood test checks for gestational diabetes, a temporary form of diabetes that develops in 3 to 8 percent of pregnancies. Women at increased risk are those who are older than age 25, are obese, have a family history of diabetes, have previously given birth to a baby weighing more than 9 pounds, or have sugar in their urine during routine testing.
• Group B streptococcus (GBS) test – This test is given later in pregnancy (usually 35 to 37 weeks) by swabbing the vagina and rectum to detect the presence of Group B streptococcus (GBS) bacteria. Although GBS bacteria are found naturally in the vaginas of many women, it can cause infections in newborns when present during the delivery. If found, an antibiotic will be given to the mother during labor to reduce the baby’s chances of exposure.
Additionally, elective tests may be performed if a mother has a specific health condition that must be monitored at the request of the mother or on the doctor’s recommendation. These tests can measure the risk level and screen for certain genetic conditions or treatable health problems in the mother that could harm her or her baby – or simply, provide more information, such as the gender of the baby. The obstetrician should always discuss the benefits and any risks associated with each test.
Elective tests include:
• Chorionic villus sampling (CVS) – The test is used to detect chromosomal disorders such as hemophilia, which prevents blood from clotting properly, or Down syndrome, which causes mental retardation and physical defects. The test is offered at 10 to 12 weeks as an alternative to amniocentesis and involves taking a tiny tissue sample from the placenta, either through the abdominal wall or cervix. CVS can be administered earlier than amniocentesis, but carries higher risks of infection, spotting/bleeding, or miscarriage (1 percent).
• Amniocentisis – Offered at 15 to 20 weeks, this test samples amniotic fluid from the womb – taken via a thin needle inserted through the belly button – and analyzes it to determine the risk for Down syndrome and other chromosomal abnormalities, structural problems such as spina bifida, inherited metabolic disorders, or common birth defects such as heart problems or a cleft lip/palate.
• Maternal blood screening/triple screen – This blood test, offered at 15 to 20 weeks, is also called a multiple-maker screening. Used to determine the risk for Down syndrome and other defects, such as spina bifida, the test calculates the amount of alpha-fetal protein (produced by the fetus) in the mother’s bloodstream and in amniotic fluid, as well as levels of two pregnancy hormones.
An expectant mother can make an informed decision about what’s right for her and her baby by learning as much as possible about the available tests, and talking with their doctor, family, a spiritual advisor and/or genetic counselor.
Remember that this information is not intended to replace the advice of your doctor, but rather to increase awareness and help equip patients with information to facilitate conversations with their physician.
For more information, visit the Health Resources link on our web site at (www.paysonhospital.com) and click on “Health Resources” and click on “P” in the Health Encyclopedia. There you will find a variety of informational articles about pregnancy and how your habits can impact your developing baby. Just found out you’re expecting? Call 928-474-9744 to schedule an appointment with one of our Obstetricians.
About the Author: Cynthia Booth, M.D. is an OB/GYN. She practices with John Dacanay, M.D. at Preferred Women’s Care, P.L.L.C., at 120 E. Main Street, Suite A in Payson. Her office number is 474-9744.
Sources: National Institutes of Health, www.nih.gov; March of Dimes, www.marchofdimes.com