The following are some of the more common tests performed during pregnancy:

What is an alpha-fetoprotein screening (AFP)?
This blood test measures the levels of alpha-fetoprotein, a protein released by the baby's liver and found in the mother’s blood. Abnormal levels of AFP may signal brain or spinal cord defects, multiple fetuses, a miscalculated due date, or Downs syndrome (a chromosomal abnormality which includes mental retardation and distinct physical features).

How is an alpha-fetoprotein test performed?
Although the specific details of each procedure vary slightly, generally, an alpha-fetoprotein test follows this process: 

Blood is usually drawn from a vein between the 15^th and 18^th weeks of pregnancy. 

The blood sample is then sent off for laboratory analysis.

What is an amniocentesis?
An amniocentesis is a procedure used to obtain a small sample of the amniotic fluid which surrounds the fetus -- to help determine chromosomal and genetic disorders and certain birth defects. An amniocentesis can also help assess the maturity of the baby’s lungs in the third trimester. An amniocentesis is routinely performed on women between the 15^th and 20^th weeks of pregnancy who are at risk for genetic disorders, including women who are over age 35. There is a slight risk of miscarriage after an amniocentesis.

How is an amniocentesis performed?
An amniocentesis is a procedure that involves inserting a long, thin needle through the mother’s abdomen into the amniotic sac to extract a small sample of the amniotic fluid for examination. The amniotic fluid contains cells shed by the fetus. Although the specific details of each procedure vary slightly, generally, an amniocentesis follows this process: 

1. The abdomen is cleaned with alcohol or iodine.
   
   
2. Your physician may give a local anesthetic so that you will not feel the needle prick in your abdomen.
   
   
3. Ultrasound is used to help guide a hollow needle into the amniotic sac.
   
   
4. A small sample of fluid is withdrawn for laboratory analysis.
   
   
5. Strenuous activities should be avoided for 24 hours following an amniocentesis.

What is a chorionic villus sampling (CVS)?
CVS, like an amniocentesis, is a prenatal test that can often detect genetic abnormalities and chromosomal disorders. However, the primary advantage of a chorionic villus sampling is that the procedure can be performed and results are available much earlier in the pregnancy than those of an amniocentesis. The procedure is usually performed between the 10^th and 12^th weeks of pregnancy.

How is CVS performed?
CVS involves inserting a needle or catheter into the abdomen or vagina to extract a small sample of placental tissue cells (chorionic villus). Although the specific details of each procedure vary slightly, generally, a chorionic villus sampling follows this process: 

1. Ultrasound is used to guide the catheter through the vagina and cervix into the placental tissues. If the trans-abdominal method is used, a local anesthetic will be given and the needle will be inserted through the abdominal wall into the placenta.
   
   
2. A small sample of tissue in the placenta will be withdrawn for laboratory analysis.
   
   
3. Strenuous activities should be avoided for 24 hours following a CVS.

What is fetal monitoring?
During late pregnancy and during labor, your physician may want to monitor the fetal heart rate and other functions. Fetal monitoring involves the use of ultrasound to measure the fetal heart rate and contractions of the uterus. External or internal fetal monitoring techniques may be used.

How is fetal monitoring performed?
Using a stethoscope to listen to the fetal heart beat is the most basic type of fetal monitoring. However, electronic fetal monitoring is now often used. Although the specific details of each procedure vary slightly, generally, fetal monitoring follows this process: 

1. If the test is performed before labor begins, the mother-to-be should eat to increase fetal movement.
   
   
2. Gel is applied to the abdomen to act as a medium for the ultrasound transducer.
   
   
3. The ultrasound transducer is attached to the abdomen with straps and transmits the fetal heartbeat to a recorder.
   
   
4. During contractions, an external tocodynamometer (a monitoring device that is placed on the stomach with a belt) can record the patterns of the contractions.
   
   
5. Sometimes internal fetal monitoring is used. Internal fetal monitoring involves inserting electrodes through the dilated cervix and attaching the electrodes to the scalp of the fetus.

What is a glucose tolerance test?
A glucose tolerance test, usually conducted in the 5^th month of pregnancy, measures levels of sugar (glucose) in the mother's blood. Abnormal glucose levels may indicate gestational diabetes.

How is a glucose tolerance test performed?
Although the specific details of each procedure vary slightly, generally, a glucose tolerance test follows this process: 

1. The mother-to-be may be asked to only drink water on the day the glucose tolerance test is given. 
   
   
2. An initial fasting sample of blood is drawn from a vein.
   
   
3. You will be given a special glucose solution to drink.
   
   
4. Blood will be drawn several times over the course of several hours to measure the glucose levels in your body.

What is a Group B strep culture?
Group B Streptococcus is an infection in the mother that can lead to complications and sometimes death in the newborn, if the infection is transmitted to the baby. Transmission of the infection can occur during delivery. Group B strep has become more prevalent in the last two decades. Physicians now routinely perform cultures on the mother’s vagina and rectum to diagnose the infection. Group B strep can easily be treated with antibiotics.

What is an ultrasound?
An ultrasound scan is a diagnostic technique which uses high-frequency sound
waves to create an image of the internal organs. Ultrasounds are routinely done once during the course of the pregnancy to ensure normal fetal growth and verify the due date. Ultrasound scans may also be performed at other times during the pregnancy:

• to diagnose an ectopic pregnancy
• to determine presence of multiple fetuses
• to diagnose a miscarriage
• to assist in prenatal tests such as an amniocentesis
• to diagnose some birth defects
• to determine size and position of a fetus late in the pregnancy

How is an ultrasound scan performed?
Although the specific details of each procedure vary slightly, generally, ultrasounds follow this process: Two types of ultrasounds can be performed during pregnancy:

pelvic ultrasound
In a pelvic ultrasound, gel is applied to the abdomen and the ultrasound transducer glides over the gel on the abdomen to create the image.

transvaginal ultrasound
In a transvaginal ultrasound, a smaller ultrasound transducer is inserted into the vagina and rests on the cervix to create an image. A transvaginal ultrasound produces a sharper image and is often used in early pregnancy.

What is genetic screening?
Many genetic abnormalities can be diagnosed before birth. Your physician may recommend genetic testing before you become pregnant or during the pregnancy if you or your partner have a family history of genetic disorders and/or you have had a fetus or baby with a genetic abnormality.

Examples of genetic disorders that can be diagnosed before birth include:

• cystic fibrosis
• Duchenne’s muscular dystrophy
• hemophilia A
• thalassemia
• sickle cell anemia
• polycystic kidney disease
• Tay-Sachs disease

What do genetic screening methods include?
Genetic screening methods may include:

• ultrasound scan
  
  
• alpha-fetoprotein test (AFP)
  
  
• chorionic villus sampling (CVS)
  
  
• amniocentesis
  
  
• percutaneous umbilical blood sampling (withdrawing a small sample of the fetal blood from the umbilical cord)

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