Prenatal Testing

Many different tests may be performed during the course of your pregnancy. Some are routine, while others may be done based on your medical history, family background, and race. All test results provide your caregiver with important information which will help with the management of your pregnancy.

Your first prenatal visit answers a lot of questions for both you and your caregiver. Information pertaining to your own health history is important to help determine potential risk factors. Your initial appointment will be longer than remaining office visits, and is likely to include the following:

Due Date Calculation
Your pregnancy is calculated to last approximately 40 weeks, or 280 days. A general estimation of when your baby is due is done as follows: Add seven days to the first day of your last menstrual period, subtract three months, add one year.

Blood Pressure
An increase in circulatory blood volume during pregnancy often affects your blood pressure. It is important to determine a normal blood pressure for you to use for comparison as your pregnancy progresses.

Breast Exam
A thorough exam of your breasts helps assess your ability to breastfeed by checking for flat or inverted nipples, as well as screens for abnormalities.

Pelvic Exam
An internal exam will confirm your pregnancy, estimate the size and shape of your pelvis and determine if the estimated due date is correct. A PapTest, to screen for cervical cancer, will be done at this time.

Weight Check
Most often, a recommended weight gain of 25-35 pounds is best, but many predisposing factors will affect how much weight you gain. Your pre-pregnant weight will be recorded, and your weight will be checked at each visit. Be assured that eating a well balanced, healthy diet will result in the right amount for you.

Urine Test
Testing of your urine provides information about your sugar and protein levels, as well as detects possible infections.

Blood Tests
Blood tests provide a great deal of information. A thorough discussion with your caregiver will determine which tests are right for you.

Routine Blood Tests – Routine laboratory tests, done early in your prenatal care, determine your blood type, check for anemia (lack of iron), sexually transmitted diseases, and Hepatitis B, as well as determine whether or not you have had German measles or mumps. Your caregiver may also recommend testing for HIV at this time.

Maternal Serum Screening Tests – These are blood tests performed to find out whether a mother has a higher-than-average risk of having a baby with certain birth defects.

Alpha-fetoprotein (AFP) – This protein is found in fetal blood and amniotic fluid. A small amount of blood is taken from the vein in the mother’s arm between 15-18 weeks of pregnancy. The test helps detect incidence of neural tube defects such as spina bifida, and Down Syndrome. Results are usually available in 1-2 weeks. Only a small number of patients whose maternal serum screening test show abnormal levels have a baby with a birth defect. Abnormal tests results are usually followed by additional diagnostic testing.

Multiple Marker Screening – This test measures levels of hormones in the mother’s blood, in addition to the AFP. It is recommended for women over 35 years of age, and is used to screen for Down Syndrome. Blood is drawn between 15-18 weeks of pregnancy, and the results are available in 1-2 weeks. Abnormal test results are usually followed by additional testing. Only 1-2% of women whose tests show abnormal results actually have babies with Down Syndrome.

Additional tests may be recommended by your caregiver for identification of genetic disorders or to check the well-being of your baby.

Ultrasound
Ultrasound is an important diagnostic tool that can provide valuable information throughout your pregnancy about the health of your baby. It is the most commonly used prenatal diagnostic procedure, and is often done between 16-18 weeks. A device is moved across the skin of the abdomen and high frequency sound waves bounce off tissues inside the body. This creates a picture of your baby on a television screen showing the skeleton and organs, umbilical cord, and placenta. An ultrasound can determine many things such as:

  • age of the fetus
  • growth progress of the fetus
  • location of the placenta
  • fetal position, movement, and breathing rate
  • amount of amniotic fluid
  • whether more than one fetus is present
  • some birth defects

Level II Ultrasound gives a more detailed evaluation of the fetus. During the second half of your pregnancy, it can be used to assess blood flow to the baby’s heart and brain, as well as the uterine and umbilical arteries.

Having an ultrasound may require some special preparation on your part. If done early in pregnancy, you will need to have a full bladder at the time of the test. Your caregiver will instruct you regarding the amount of water you need to drink prior to the test.

Amniocentesis
This informative diagnostic test is usually done between 16-18 weeks of pregnancy. It can be performed either in the doctor’s office, or as an outpatient hospital procedure. During amniocentesis, using sterile instruments and the aid of ultrasound, a thin needle is guided through the abdomen. A small sample of amniotic fluid is withdrawn from the amniotic sac and sent to a lab to test for chromosomal abnormalities. Because amniocentesis involves the study of chromosomes, your baby’s sex can also be determined. Results are available within 3 weeks from the time of the test. Complications from this procedure are rare, but may include cramping, vaginal bleeding, and leaking of amniotic fluid after the test. Later in pregnancy, amniocentesis may be used to determine fetal lung maturity. In this instance, test results are available within a few days.

Chorionic Villus Sampling (CVS)
Chorionic villi are tiny, fingerlike projections of tissue that make up the placenta. CVS can be performed in the doctor’s office or a hospital setting. This test involves the removal of a small sample of tissue by a catheter inserted through the vagina and cervix, or through a needle inserted into the abdomen and placenta. The villi are sent to the lab, grown in a culture and analyzed. CVS detects some of the same chromosome problems as amniocentesis, but can be done earlier in pregnancy, usually between 10-12 weeks. Results of CVS are available within 3 weeks. Risks are rare, but the most common one is miscarriage. It is estimated that 1% of women who have CVS will have a miscarriage they would not have otherwise had.

Monitoring the fetal heart rate and activity during pregnancy gives your caregiver important information. Within weeks after your pregnancy has been confirmed, your caregiver will listen to your baby’s heartbeat at each prenatal visit. This is done with a small device that transmits sound waves through your abdomen, picking up the sound of your baby’s heart. The following tests use monitoring of your baby’s activity level and heart rate to determine how your baby is doing.

Kick Counts
Your caregiver may ask you to keep track of your fetus’s movements or kicks. This is a simple way to help determine fetal well-being during the last trimester of your pregnancy. There are varying ways to do this and your caregiver will tell you which way is best for you.

Non-stress Test
This test measures fetal heart rate in response to fetal movement. Usually, a baby’s heart rate increases as the baby moves. Changes in the heart rate are considered a good sign. During this test, you lie in a comfortable position with a monitor belt around your abdomen. Each time you feel the baby move, you push a button which records on a strip of paper. Your caregiver then evaluates your baby’s movement in relation to your baby’s activity. The length of this test varies depending on how long it takes before the baby is awake and active, but on average it takes 20-30 minutes to complete.

Contraction Stress Test
This test measures how the fetal heart rate reacts to the uterus when it contracts. It is done to determine placental function and can take up to two hours to complete. When the uterus contracts, there is a temporary decrease of blood flow to the placenta. To perform this test, the mother is either given a drug called oxytocin to make her uterus contract, or she is told to rub one of her nipples lightly, which causes her body to release oxytocin naturally. The response of the fetal heart rate in relation to the contraction is recorded and evaluated by your caregiver. If the placenta is working well, contractions do not cause a drop in fetal heart rate, but if placental function is lessening, a drop in fetal heart rate is seen. This is used to decide whether the baby should be delivered earlier than the expected due date.

Biophysical Profile
This test combines electronic fetal monitoring with an ultrasound. It is used to examine the fetal heart rate, muscle tone, body movement, and the amount of amniotic fluid present. It also checks fetal breathing movements. This is a simple test that can be repeated as necessary to check the progress of your pregnancy.

Your own health history may never require many of the above mentioned tests. Be assured that with proper communication between you and your caregiver, only those tests best suited for your situation will be recommended. This will help assure the ultimate goal for your pregnancy – healthy mom and baby!

Editorial provided by Mary Shanahan, RN, CES and Pat DiGiacomo, RNC, MSN. Both women are perinatal education coordinators at North Penn Hospital in Lansdale, Pennsylvania.