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During pregnancy, there are many prenatal tests that your OB/GYN may recommend or you may learn about through family and friends. Not all prenatal tests are recommended for all pregnancies, so it can be confusing at first to understand which ones you will need. Ultimately, your doctor can explain which tests are right for you, but here are some of the basics of prenatal tests.

What Are Prenatal Tests?

Prenatal tests are any type of screening or diagnostic test that your OB/GYN may recommend during your pregnancy. These are performed to check in on both your and the baby’s health as well as screen for genetic conditions or birth defects throughout pregnancy. Many tests are recommended for all pregnancies, while others are only recommended for those at a higher risk for certain conditions. Prenatal tests fall into two categories: screening tests and diagnostic tests.

Screening Tests

Screening tests can determine whether your baby is more likely to have a condition but are not designed to determine whether they have that health condition.

Diagnostic Tests

Diagnostic tests are generally performed after a screening test to confirm whether your baby has a given health condition. Certain diagnostic tests have significant risks, including miscarriage, which is why screening tests are performed first. However, a diagnostic test can help parents be prepared to care for their baby’s health as soon as they are born or give them more time to make decisions regarding their baby’s care.

Prenatal Tests Throughout Pregnancy

Several common prenatal tests are performed throughout a pregnancy. Your prenatal tests throughout your pregnancy are often like tests you receive at a normal annual physical. These include:

• Blood tests, which are performed to check for infections like syphilis, hepatitis, B, or HIV, conditions like anemia or Rh disease, and crucial health information your doctor needs to know like your blood type.
• Urine tests, which are performed to check for infections, such as a bladder or kidney infection, and screen for conditions like preeclampsia.
• Blood pressure checks, which can help screen for preeclampsia.
• Weight checks to ensure you are gaining a normal amount.

Prenatal Tests During the First Trimester

The prenatal tests you have during your first trimester depend on your specific needs and personal preferences. Your OB/GYN can help you choose which are best for you. During the first three months of your pregnancy, you may have any of the following tests.

• Early ultrasounds are performed to confirm the location and health of the pregnancy. Also importantly, measurements are taken to determine how many weeks into pregnancy.
• Carrier screening for genetic conditions. Even though a mother may be healthy, she can be a carrier of a genetic disorder. If the father is a carrier of the same genetic disorder, two apparently healthy can produce a child with significant genetic disease.  The screening starts with the mother and if she is not a carrier of any genetic disease, the testing ends there. If she is a carrier of one or more genetic diseases, the father is then carrier tested for the same diseases.  If he is negative, there is no risk for the child. If he also is a carrier of the same disease, there is usually a 25% chance of having a child with the genetic disease, and a diagnostic test is offered.
• Cell-free fetal DNA testing, or noninvasive prenatal screening. This test looks at your baby’s DNA for genetic conditions such as Down syndrome and is done after nine weeks of pregnancy.
• First Trimester Screening is done between 11 and 13 weeks. This test is to screen for the most common genetic disorders including Down Syndrome, Trisomy 18, and Trisomy 13.  This test utilizes both ultrasound and blood parameters to identify fetuses at risk for those genetic disorders.  The ultrasound component involves a measurement taken at the back of the neck and identifying a calcified nasal bone.  The blood component of this test is variable but usually a combination of hormones.  A computer is used to determine the risk of those genetic disorders based upon the mother’s age, the ultrasound findings, and the hormone levels.  If this test returns high risk, an invasive diagnostic test is offered.
• Chorionic villus sampling (CVS), is the earliest invasive diagnostic genetic test available. A small sample to tissue is obtained from the placenta to check for genetic conditions. It is performed at 10-13 weeks of pregnancy.

Prenatal Tests in the Second Trimester

During the fourth, fifth, and sixth months of your pregnancy, the following tests may be recommended.

• Ultrasounds are commonly performed between 16-22 weeks of pregnancy to check in on your baby’s growth, placental location, and an anatomic survey to screen for birth defects.
• Glucose screening is usually performed between 24 and 28 weeks to screen for gestational diabetes.
• Quad screen blood tests are being done less frequently as other better tests have replaced them. It checks for signs of birth defects by measuring four substances in the blood: AFP, hCG, and inhibin A and is done at 15-22 weeks.
• Amniocentesis is an invasive diagnostic test where a specimen of the amniotic fluid is obtained and checked for genetic conditions.

Prenatal Tests During the Third Trimester

During the final three months of pregnancy, there are far fewer optional tests. Commonly, your OB/GYN will be repeating tests for infections that could affect the fetus and newborn baby.  They will also do a group B strep test during the final few weeks of pregnancy for the same reason.

Schedule an Appointment

To schedule an appointment with an OB/GYN, call Carnegie Women’s Health in New York City or contact us online.

Source: “Prenatal Tests” March of Dimes, https://www.marchofdimes.org/pregnancy/prenatal-tests.aspx

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!