Second Trimester Prenatal Tests

You may be offered several prenatal tests throughout your pregnancy. Some tests are performed routinely on all pregnant women, such as blood tests to determine blood type and iron levels. Some tests are done to screen women for a condition they or their baby are at risk for developing. Other tests, such as Chorionic Villus Sampling (CVS) and amniocentesis, are considerations for women 35 years of age and older or those who may be at risk of delivering a baby with certain birth defects. Some tests are done later in pregnancy to measure the baby’s well-being and to make sure that the baby is growing and developing at the expected rate.

The following is a brief description of some of the more common prenatal tests. Your healthcare provider, and sometimes a genetic counselor, can help you determine which tests might be recommended for your pregnancy and help you when making decisions.

Quadruple Marker

The quadruple marker is a screening procedure that measures the amount of four substances in your blood:

• Alph-fetoprotein (AFP)
• Unconjugated estriol(uEST)
• Human chorionic gonadotropin (hCG)
• Analyte inhibin (Inh)

Studies show that women with pregnancies affected with Down syndrome have lower serum of AFP and uEST and higher levels of hCG than women with unaffected pregnancies.

The tests can be done using a small sample of your blood sometime between 15 and 20 weeks of pregnancy, counting from your last menstrual period. Results are usually available in 1 to 2 weeks. If the results are abnormal, further testing (such as ultrasound and amniocentesis) may be suggested.

Expanded Alpha-Fetoprotein (AFP)

Expanded AFP is a simple blood test performed between 15 and 20 weeks of pregnancy. The test provides information about the risk of neural tube defects, such as spina bifida, Down syndrome and other genetic problems.

Who should consider Expanded AFP?

The state of California recommends that this test be offered to all pregnant women.

How is the screening performed?

The test is performed through a simple blood test ordered by your healthcare provider.

What type of problems can be detected?

The test provides information about the risk of neural tube defects, such as spina bifida, and chromosome disorders in the developing baby.

Is the blood test ever wrong?

It is important to note that the Expanded AFP test is only a screening test, not a diagnostic test. There will be a group of women who receive a false positive or “false alarm.” Most women who test positive are carrying a healthy baby. The only way to tell a false positive result from a true birth defect is through diagnostic testing. Women with a positive test result are offered amniocentesis as a diagnostic test. A genetic counselor can help explain the benefits and limitations of the Expanded AFP blood test compared to diagnostic tests.

Ultrasound (sonogram)

In an ultrasound procedure, a device known as a transducer is placed on your abdomen. The device directs high frequency sound waves at your developing baby. The echoes created by the sound waves are turned into visual images of the baby’s limbs, organs and other internal structures that can be seen on a monitor.

Will an ultrasound hurt the baby?

Extensive studies to date show no evidence of ill effects or harm to the baby by these sound waves.

What can ultrasound detect?

An ultrasound test can detect:

• Many birth defects early in pregnancy that otherwise would go undetected until birth
• Number of babies present
• Baby’s growth
• Confirmation of due date
• Placental position
• Other information about your pregnancy that can be useful to you and your healthcare provider

What is a fetal echocardiogram?

A fetal echocardiogram is a detailed ultrasound evaluation of the baby’s heart structure. It is performed in pregnancies at increased risk for congenital heart disease. Fetal echocardiograms can detect most cases of serious, life threatening congenital heart problems.

What is a targeted ultrasound examination?

A targeted ultrasound examination looks at a specific organ system or part of the body. It is used to try to detect any trouble before birth in pregnancies at increased risk for specific genetic or physical problems. As with many medical tests, ultrasound is not perfect. Because of factors that can develop later in pregnancy or interfere with the ability to clearly see all of the baby’s internal structures, an ultrasound will not detect all birth defects.

Does an ultrasound hurt?

You should not feel pain of any kind as this is a non-invasive test.