Experts agree that a woman should begin to undergo routine screening tests either before conception or at her first prenatal visit. These tests alert doctors to potential problems and provide a basis for comparison as the pregnancy progresses. Here are some straightforward answers to questions about the most common tests during pregnancy, their risks and why they are necessary.
Here are some tests you may undergo during the first trimester of your pregnancy:
Blood tests: During one of your initial examinations, your doctor or midwife will identify your blood type and Rh (rhesus) factor, screen for anaemia, check for immunity to rubella (German measles), and test for hepatitis B, syphilis, and HIV. Depending on racial, ethnic, or family background, you may be offered tests and genetic counselling to assess risks for diseases such as Tay-Sachs, cystic fibrosis, and sickle cell anaemia (if these weren’t done at a preconception visit). Tests for exposure to diseases such as toxoplasmosis and varicella (the virus that causes chickenpox) may also be done if needed. Your health care provider may also want to check your levels of hCG, a hormone secreted by the placenta, and/or progesterone, a hormone that helps maintain the pregnancy.
Urine tests: You will also be asked early on for a urine sample so that your doctor or midwife can look for signs of kidney infection and, if necessary, to confirm your pregnancy by measuring the level of hCG. (A blood hCG test to confirm pregnancy may be used instead.) Urine samples will then be collected regularly to detect glucose (a sign of diabetes) and albumin (a protein that may indicate preeclampsia, which is pregnancy-induced high blood pressure).
Chorionic villus sampling (CVS): If you’re 35 or older or have a family history of certain diseases, you will be offered this optional, invasive test usually between 10 and 12 weeks of pregnancy. CVS can detect many genetic defects, such as Down’s syndrome, sickle cell anaemia, cystic fibrosis, haemophilia, and muscular dystrophy. The procedure involves either threading a tiny catheter through your cervix or inserting a needle into your abdomen to obtain a tissue sample from the placenta. The procedure carries a 1% risk of inducing miscarriage and is about 98% accurate in ruling out certain chromosomal birth defects. But, in contrast to amniocentesis, it does not help in detecting neural tube disorders, such as spina bifida and anencephaly, or abdominal wall defects.
A promising new procedure that combines a blood test with an ultrasound to screen for Down’s syndrome may be available between 11 and 14 weeks of pregnancy. The results of a blood test that measures hCG and/or PAPP-A (pregnancy-associated plasma protein A) in maternal blood are used with an ultrasound measurement of the skin at the back of the foetus’ neck (called nuchal translucency). The procedure may be able to pick up a substantial portion of Down’s syndrome cases and other genetic conditions. However, as with all screening methods, a more invasive diagnostic technique like CVS is used to follow up a positive screen.
Tests for glucose, protein and blood in the urine to detect problems such as impaired kidney function and diabetes
A cervical culture for gonorrhea and chlamydia
Blood tests to determine blood type and Rh type (to test for Rh incompatibility) and to check for anemia
Tests for rubella and toxoplasmosis (a parasitic infection) and hepatitis B
Chorionic Villus Sampling (CVS) detect defects in the fetus as early as the ninth week of pregnancy. The problem: The possible risk the test poses. Studies conducted in 1992 yielded conflicting results concerning the safety of CVS. Researchers at Michael Reese-Humana Hospital in Chicago found a higher incidence of limb defects in babies born to women who had undergone CVS. However, most other studies, including a later one conducted by researchers at Jefferson Medical College in Philadelphia, found CVS to be safe. Before having CVS, discuss the benefits and risks of the procedure with your doctor, and don’t be afraid to request a second opinion.
Blood tests–to determine your blood type, whether you are Rh negative or positive, and whether you have antibodies in your blood that might increase the likelihood of your baby being anemic or jaundiced as a newborn.
The Importance of Rh Factor
You may have lived your entire life without knowing whether your blood has the so-called Rh factor and not think anything of it. However, during pregnancy it’s important information. Your genes determine whether or not your red blood cells have this type of protein. Rh factor has no importance to your health before you become pregnant.
When you are pregnant, if you do not have the Rh factor (that is if you are “Rh negative”) and if your baby’s does (if he’s “Rh positive”), problems can arise. Your immune system may recognize your baby’s blood as a foreign substance and produce antibodies that can result in fetal damage or death. This occurs most often during the second and later pregnancies of Rh-negative moms. Your first child will usually not be affected by it. By testing your blood, your doctor can discover if your blood is making antibodies. If this is the case your doctor can give you an injection to prevent antibodies from forming and prevent fetal damage or death.
• Pap smear–to test for the risk of developing cervical cancer.
• Urinalysis–to ensure that you don’t have a bladder or kidney infection or diabetes.