Your Second Trimester
Testing and Exams
The following are common tests done within the second trimester of your pregnancy:
- AFP (Alpha-Fetal Protein) or Serum Triple Test
- Ultrasound or Sonogram
- Amniocentesis
- Glucose Tolerance Test
AFP (Alpha-Fetal Protein) or Serum Triple Test
The AFP blood test is done at 15 to 20 weeks of pregnancy. It is designed as a risk estimate for Down syndrome and certain chromosomal abnormalities, such as neural tube defects, spina bifida, trisomy 21 and trisomy 18. AFP does not detect all cases of these birth defects. Down syndrome detection rate is age-dependent. Most women with a positive test are carrying a healthy baby.
The following tests are performed in the maternal serum triple test:
The screening is based on studies showing that women with pregnancies affected by Down syndrome have lower serum levels of AFP and uEST and higher levels of hCG than women with unaffected pregnancies. The tests are done on a small blood sample from the mother between 15 and 20 weeks of pregnancy. If the results are abnormal, further testing, such as an amniocentesis, may be suggested.
You will receive the Expanded AFP Screening Program booklet. You can also download the booklet from the California Department of Health (.pdf) (accessed October 2007). Genetic Disease Screening Program information is available in Spanish and English (California Department of Health Services, accessed October 2007).
It is important to note that the AFP is only a screening test. A positive result does NOT confirm a definite problem, it simply identifies a pregnancy at increased risk. Most women with an abnormal result are carrying a healthy fetus. Your doctor will determine the appropriate time to have the test.
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Ultrasound or Sonogram
Ultrasound uses sound waves to produce a picture. It is performed using an instrument placed on the outside of your abdomen or transvaginally. The detailed study for the second trimester is usually scheduled in the Radiology Department. No harmful effects have been reported from this test during more than two decades of use.
This test may be used to evaluate many aspects of pregnancy at any time during pregnancy. Most commonly, ultrasound is used for a routine anatomy scan of the fetus at 18 to 20 weeks. In addition to viewing most of the baby's physical features, it also may determine fetal position, size (age) and gender, amount of amniotic fluid and location of the placenta.
Occasionally, a mother's body or baby's position may prevent optimal viewing of a particular feature and a repeat scan will be needed. You may choose to know your baby's gender, although ultrasound is not 100 percent accurate in determining gender. You may also have another family member, friend or the baby's sibling(s) present.
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Amniocentesis
Amniocentesis is used for the purpose of determining certain chromosomal abnormalities and other types of serious birth defects, which would require special care during pregnancy, delivery and beyond. It is strongly encouraged for mothers over 35 years old and those with certain family histories. It is generally done between the 14th and 17th weeks of pregnancy.
Amniocentesis involves withdrawing and testing a small amount of the amniotic fluid surrounding the fetus. Some of the tests performed on the amniotic fluid include:
- Rh disease, or incompatibilities between mother and baby blood types
- Genetic defects such as Down syndrome
- Defects associated with abnormal brain and spinal cord development, (called neural tube defects).
You may also find out the fetus' gender, although amniocentesis is never done solely to determine a baby's sex.
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Glucose Tolerance Test
Glucose Tolerance Test (GTT) is a simple blood test used to screen for gestational diabetes. The hormones of pregnancy may alter your body's ability to manage sugars and carbohydrates, leading to the condition. This may result in the growth of an abnormally large baby with difficulties at birth. We routinely screen all women between 24 and 28 weeks to determine risk for gestational diabetes. Your doctor may order this test earlier if you have history of gestational diabetes or other risk factors.
Screening can be done as either a one- or two-step process. At PAMF we use the two-step process.
Your physician or nurse practitioner may provide you with a concentrated sugar solution. You may also get the sugar solution from the laboratory where the test is scheduled. You will be instructed to drink the solution, then go to the laboratory within one hour. Your blood will be drawn to determine how well your body uses or metabolizes the sugar. Diabetes exists when there is a high amount of sugar in your blood (blood glucose) due to the body's failure to handle the sugar in a normal fashion.
If the results of this test indicate that your blood sugar is high, a second test, called the OGTT (Oral glucose tolerance test) is ordered. You will be instructed to return to the lab on another day, after following a three day diet. You will arrive at the laboratory after fasting for 12 hours prior to the scheduled test. This means that you are to have nothing to eat or drink in the 12 hours prior to the test, except water. A blood glucose test will be drawn. You will again be instructed to drink a concentrated sugar solution, which the laboratory will provide. Blood tests will be drawn at one-hour intervals for three hours. If two out of the four blood tests show an elevated blood sugar, gestational diabetes is diagnosed.
Fortunately, the vast majority of women who develop this condition can still have a safe pregnancy with a healthy baby by going on a special diet with frequent blood sugar checks. Some women will require insulin to manage their gestational diabetes.
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