Prenatal Testing
When? Routine blood tests are usually ordered at your first prenatal visit with your caregiver.
How? Small samples of blood will be drawn, usually in a lab.
Why? Routine blood tests screen for a variety of things, such as blood type, Rh factor, anemia, diabetes, hepatitis, HIV or AIDS and rubella immunity status. Your glucose, iron and hemoglobin levels will also be monitored. If ordered by your care provider, your blood may also be screened for sexually transmitted diseases, including genital herpes, gonorrhea and Chlamydia.
When? You will be asked to provide a midstream urine sample at each prenatal visit.
Why? The urine test is used to monitor your glucose (sugar), protein, ketone and bacteria levels. This helps your caregiver determine if you have a bladder or kidney infection, dehydration, pre-eclampsia or diabetes. Changes in these levels later in pregnancy may indicate gestational diabetes (high sugar level) or urinary tract infection or pre-eclampsia (high protein level). Your doctor will be best able to treat these conditions if they are detected as early as possible.
When? The First Trimester Screen is given between the 11th and 13th week of pregnancy.
How? A blood sample is drawn from the mother, followed by an ultrasound. Results are usually calculated within a week of testing. The blood test indicates the level of two pregnancy-related hormones (hCG and PAPP-A) while the ultrasound measures the amount of fluid under the skin behind the baby’s neck.
Why? This new test is usually given to mothers who are deciding between first-trimester genetic testing, such as a chorionic villus sampling (CVS), or second-trimester genetic testing (amniocentesis). This is currently the earliest and only non-obtrusive test used as a screen for abnormalities such as Down syndrome. A positive result does not necessarily indicate that an abnormality exists. Instead, it is an indicator that further testing may be required.
When? CV sampling is taken between 12 and 14 weeks of pregnancy.
How? A sampling of chorionic villi cells are removed from the placenta where it attaches to the wall of the uterus. This is done in one of two ways, depending on the shape of the uterus and the placement of the placenta:
Transcervical CVS – using the ultrasound as a guide, the doctor will insert a catheter through the vagina and cervix to the edge of the placenta. A small amount of tissue is removed through the tube. This is the more common method of CVS.
Transabdominal CVS – using an ultrasound as a guide, a thin needle is inserted into the abdominal wall to the placenta. Tissue samples are drawn through the needle. The tissue is then sent to a lab for analysis. Results are usually available within seven days.
Why? CVS is a diagnostic test that identifies several chromosomal abnormalities, such as Down syndrome, or genetic disorders, including cystic fibrosis. CVS can also provide genetic material for pre-birth paternity testing. Many women prefer CVS because it is done earlier in the pregnancy than amniocentesis.
Any risks or side effects? Historically women have been told there is a 1% chance of miscarriage with the CVS; however, the March of Dimes reports that risk has declined as doctors have gained experience with the procedure.
Other side effects include spotting, cramping, infection or some pain at the needlepoint. These are usually temporary and go away without a further problem.
When? The procedure may be done once or several times during the pregnancy, based on the mother’s needs and the doctor’s orders. Most often, one ultrasound is given early in the pregnancy to determine your baby’s age. Other ultrasounds may be ordered for medical reasons.
How? Sound waves are directed through your abdomen to your baby using a device known as a transducer. The echoes of the waves translate into a visual image of the embryo’s head, limbs, organs, and other internal structures.
Why? Ultrasound can be used to determine the baby’s age and to confirm the due date. It can also show if there are multiple embryos and the placement of the placenta. Sometimes a caregiver will order an ultrasound to diagnose birth defects, evaluate baby’s well being and monitor movement and growth.
When? Formally known as the Glucose Challenge Screening and Glucose Tolerance Test, screening for gestational diabetes is usually ordered at 24 to 28 weeks of pregnancy.
How? You’ll be given a sweet liquid (glucose) to drink, then have your blood drawn after an hour has passed. If the sugar level in your blood is high at this point (when the sugar levels peak), you’ll be given the second, longer glucose tolerance test.
The second test follows a period of fasting (usually 12 or more hours) and is done on an empty stomach. First, blood is drawn to measure your baseline fasting glucose level. Then you will be given another, more concentrated glucose solution to drink. Your blood will be drawn every hour for the next three hours, to evaluate how your body processes sugar.
Why? Both the glucose screening and the glucose tolerance test check for gestational diabetes. This is a form of diabetes that develops during pregnancy for some women. Currently, 3% to 8% of pregnancies in the United States involve gestational diabetes, which if left untreated could lead to health problems for the baby, the mother or both.
Usually if one of the three blood tests come back high (or “positive”), your caregiver will instruct you to change your diet, then retest later in the pregnancy. If two or more of the tests are high or positive, you’ll be diagnosed with gestational diabetes. Your caregiver will develop a treatment plan specific to your situation.
When? An amniocentesis (also known as an “amnio”) is usually performed between 14 and 20 weeks of pregnancy. It is not a routine test; instead, your caregiver may suggest it if you fall into one of the following “risk” categories for chromosomal abnormalities, structural defects or other genetic disorders:
- advanced maternal age (over the age of 35)
- a family history of genetic disorders in either parent
- had an abnormal screening
- had a previous child with a birth defect
- had an earlier pregnancy with a neural tube defect or chromosomal abnormality
How? Guided by the images on an ultrasound screen, the doctor inserts a thin needle into the amniotic sac at a safe location. A small sample of amniotic fluid (about an ounce) is removed through the needle. Cells in the sample placed in a special culture, grown and analyzed. Depending on why the test is being given, results may be available from a week to two weeks from the test.
Why? Amniocentesis is most often given to detect chromosomal abnormalities such as Down syndrome, genetic disorders such as cystic fibrosis and structural defects such as spina bifida. Amnio may also be given to detect inherited metabolic disorders or to test the maturity of the baby’s lungs to determine if the child would be viable outside the womb. DNA collected in the amniotic fluid can be tested in cases where paternity is in question.
Amniocentesis is an extremely accurate indicator for the disorders listed, but there are risks involved. The risk of miscarriage ranges between 1 in 400 and 1 in 200, depending on the facility. There is also a low risk of uterine infection, leakage of amniotic fluid and injury to the fetus.
Also known as Maternal Serum Alpha-Fetoprotein Screening (MSAFP)
When? MSAFP (AFP) is a screening test, usually performed between the 14th and 20th week of pregnancy. It is often part of the triple screen test. As with all screens, this test does not diagnose a problem, instead, it indicates the need for further testing.
How? Blood is drawn from the mother’s arm and sent to a laboratory for analysis. The test examines the level of alpha-fetoprotein, which is found in the fetal serum and the amniotic fluid. The test measures the high and low levels of AFP. This result, combined with maternal age and ethnicity, is used to ascertain the risk for certain genetic disorders.
Why? The AFP is routinely offered to pregnant women, particularly those in high-risk groups for genetic abnormalities. Most women use it as a tool to help determine if they want to pursue diagnostic genetic testing, such as chorionic villus sampling (CVS) or amniocentesis.
Also known as Multiple Marker Screening
When? The triple screen is usually given between the 15th and 20th week of pregnancy. It is usually most accurate when given between the 16th and 18th week.
How? A blood sample is taken from the mother and sent to a laboratory for analysis. Three specific substances in the blood are measured during the analysis. These are:
- hCG – human chorionic gonadotropin, a hormone produced in the placenta
- AFP – alpha-fetoprotein, which is produced by the fetus
- Estriol – a hormone (estrogen) produced by the placenta and the fetus
Why? The triple screen is primarily used as an indicator that further testing may be desirable. The test screens for genetic disorders and chromosomal abnormalities. It may also be used to identify multiple pregnancies and gestational age.
High and low levels of AFP and abnormal levels of hCG and estriol are identified in the screen. These results, combined with other risk factors such as maternal age, weight, and ethnicity, help determine the probabilities of potential genetic disorders. Low levels of AFP and abnormal levels of hCG and estriol may indicate that the baby has Down syndrome, Edwards Syndrome or other chromosomal abnormalities.
High levels of AFP may indicate that the baby has spina bifida or other neural tube defects. However, inaccurate dating of the pregnancy can lead to variances in the AFP level. It is important to remember this test is merely a screen and not used for diagnostic purposes.
Also known as Quadruple Screen or Quadruple Marker
When? The quad screen is a blood test given between the 15th and 20th week of pregnancy. Results are most reliable when the test is given between the 16th and 18th week.
How? Blood is drawn from the mother and sent to a lab for analysis. Very similar to the triple screen, the quad screen measures AFP (alpha-fetoprotein), estriol, and hCG (human chorionic gonadotropin) present in the blood. It also measures a fourth substance, Inhibin-A, a protein produced by the placenta and ovaries.
Why? The quad screen is another screen – not a diagnostic test. Because of the inclusion of Inhibin-A, the test is somewhat more reliable for identifying pregnancies at risk for Down syndrome. Again, this test only indicates if a mother is at risk. It should be used as a tool in determining if diagnostic testing, such as amniocentesis, should be pursued.
Also known as Cordocentesis
When? Percutaneous umbilical blood sampling is done after 17 weeks of pregnancy. It is usually done when results from amniocentesis, CVS or ultrasound were unavailable or inconclusive.
How? The procedure is similar to an amniocentesis; however, instead of amniotic fluid, fetal blood is drawn through the umbilical cord for examination.
Using an ultrasound image as a guide, a doctor inserts a thin needle through the mother’s abdomen and uterine walls into the umbilical cord. A small sampling of blood is extracted and sent to a lab for analysis. Results are usually available within three days of the procedure.
Why? The test is used when previous test results prove inconclusive. It may be used when an abnormality has been noted on an ultrasound. Cordocentesis is sometimes used when the fetus may have an Rh disease or if the mother has been exposed to an infectious disease which may affect the baby.
The results of this test can diagnose a variety of concerns, including chromosomal abnormalities (like Down syndrome) or blood disorders. It may also be performed to diagnose malformations of the fetus, fetal infection (when the mother has been exposed to an infectious disease) or fetal platelet count in the mother. Neural tube defects, which are diagnosed through amnio, cannot be diagnosed through cordocentesis.
When? A biophysical profile is commonly done in the third trimester of pregnancy to determine the health of the baby. The test consists of two parts, the nonstress test, and the ultrasound evaluation. This test is not routine, but one or both parts may be ordered if the pregnancy is high risk or if there is any question about the fetal well being.
How? The nonstress test is performed by attaching two belts to the mother’s abdomen. One belt measures the fetal heart rate while the other monitors the presence of contractions. Usually, the baby’s movements and heart rate will be monitored for twenty to thirty minutes. The baby’s heart rate should increase after movement. If the baby does not move during this time, it does not indicate a problem, as she may be sleeping. Sometimes a buzzer or other noisemaker is used to wake the baby.
The ultrasound is performed by placing some gel on the mother’s abdomen, then sending sound waves through the abdomen into the uterus. The sound waves bounce off the baby and return an image of the fetus to the transducer. In this way, the technician can “see” the baby.
Why? A BPP is performed to learn and keep track of the baby’s health. It is also performed because of the mother’s health, in situations such as:
- You have hyperthyroidism, chronic kidney disease or lupus.
- You have developed gestational diabetes, Type 1 diabetes or high blood pressure.
- You have pre-eclampsia.
- There is too little or too much amniotic fluid present.
- You’re pregnant with multiples.
- You have passed forty weeks of pregnancy.
Usually, the BPP monitors five distinctive fetal attributes. These include breathing, movement, muscle tone, heart rate, and amniotic fluid. The test scores help the caregiver determine the baby’s health and well being and may cause them to adjust the baby’s due date.
When? Routine screening for the presence of Group B Streptococcus is performed between the 35th and 37th week of pregnancy.
How? The caregiver swabs the mother’s vagina and rectum. The sample is then sent to a lab where the culture is studied for the presence of Group B strep. Results are usually available within two days.
Why? Although the presence in Group B strep in adult women is common (the bacteria is usually found in the lower intestine or vagina of 15 to 40 percent of healthy adult females), there is a danger that the bacteria could be passed to the baby at birth. In the US, one in every 3000 babies is affected by GBS, according to the March of Dimes.
There are two types of Group B strep infection – early onset and late-onset. Please discuss the symptoms and treatments with your caregiver if you are concerned about Group B strep. Many women who test positive for Group B strep can take antibiotics during delivery to significantly decrease the chances of your baby becoming ill.