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The Importance of Prenatal Tests and Screenings in Pregnancy

A female doctor and a pregnant woman are both wearing protective masks during a prenatal medical exam

When you are pregnant, you will undergo all sorts of screenings and tests during your prenatal appointments. While being poked and prodded throughout your pregnancy may feel like a nuisance, these tests provide valuable information about your health and the health of your baby.

“The screenings and tests that take place during your pregnancy are one of the most important components of your prenatal care,” says University Hospitals OB/GYN and genetic expert Jane Corteville, MD. “The results will inform your care plan, helping your provider tailor your prenatal care to meet your individual needs and helping you make decisions related to your pregnancy and childbirth experiences.”

Prenatal tests will take place throughout your pregnancy, starting at your first prenatal appointment and continuing through the second and third trimesters. Most of them are simple and painless procedures, though some – such as certain genetic diagnostic tests – are more complex.

Read on to learn about some of the most common tests you may encounter during your pregnancy.

First Trimester Tests and Screenings

During your first prenatal appointment – typically around weeks 11 to 13 in a low-risk pregnancy – your provider will conduct a number of tests and screenings. These include:

Blood test: A complete blood panel tests for things such as blood type and RH factor, sexually transmitted diseases, optional genetic screenings, and other tests as ordered by your provider.

Urine test: You will be asked for a urine sample to test for infections that could affect your pregnancy.

Pap test: If you have not had a recent pap test, your provider may perform one to test for cervical abnormalities.

Ultrasound: An ultrasound may also be done to help your provider determine how far along you are in your pregnancy and if development is on track. You will be able to see your baby for the first time and should be able to see its heart move if you are after 7 weeks.

Second and Third Trimester Tests and Screenings

Additional tests will be done during the second and third trimester that will help make sure you are healthy and that your baby is growing and developing normally. These tests include:

The anatomy ultrasound, done between 19 and 21 weeks, provides a detailed look at your baby’s anatomy, taking measurements of many of the body parts and organs. This scan will help determine if your baby developing normally, and you can usually find out the sex of your baby at this time if you choose to do so. Occasionally, more than one scan is needed to obtain all the measurements needed.

The 1-hour glucose tolerance test is used to screen for gestational diabetes. It is usually conducted between 24 and 28 weeks, or sooner if you have a history of gestational diabetes or other risk factors. This test involves drinking a sugary drink and having your blood tested one hour later.

If your glucose level is too high, you may need to take the three-hour glucose tolerance test. This test involves a fasting blood draw, plus three additional blood tests one, two, and three hours after drinking a glucose drink. If two or more of those numbers are out of the normal range, you are diagnosed with gestational diabetes. Women with gestational diabetes need to monitor and control their blood glucose levels during the remainder of their pregnancy, through diet and exercise and/or medication.

A group B strep test is a vaginal and rectal swab taken during your third trimester that tests for group B streptococcus (GBS), a common type of bacteria that can live in the body. It is generally harmless to adults but can be dangerous to your baby if passed to him or her during delivery. If you test positive, you will receive IV antibiotics during labor in order to prevent infecting your baby.

Your provider may order a non-stress test if you are overdue, have been feeling the baby move less than usual, or have other complications or conditions that make you high-risk. During the test, two belts will be placed on your stomach – one that measures the baby’s heart rate and one to measure contractions. Your provider will watch to see if the baby’s heart rate increases when he is active.

Alternatively, your provider may order a biophysical profile. This is a test done with an ultrasound machine looking at the baby’s breathing movements and muscle tone. It gives slightly different information than the non-stress test but is also used for women with pregnancy complications.

Genetic Screenings and Tests

Starting in the early stages of your pregnancy, you can screen and test for certain birth defects and genetic disorders in your baby, such as Down syndrome and neural tube defects.

“Prenatal screenings are usually simple blood tests, or blood tests combined with an ultrasound evaluation, that can inform you of the likelihood of your baby having a genetic defect or disorder, but cannot diagnose it,” said Dr. Corteville. “Further testing may be recommended if your screening indicates a high risk of an abnormality.”

Screening options include:

The first trimester screen: Taking place around weeks 11 – 13, this is a simple blood sample combined with an ultrasound to estimate the risk of Down syndrome, trisomy 18, and trisomy 13. It can also identify other potential obstetric problems such as a higher risk for growth restriction.

Quad or Tetra screen: The second trimester screen (Quad or Tetra screen) uses a blood draw to estimate the risk of Down syndrome and trisomy 18. This test is usually offered from 15 – 20 weeks to women who have missed the first trimester screen.

Noninvasive prenatal screening (NIPS): NIPS is a blood test given after 10 weeks that screens for chromosomal disorders such as Down syndrome, Trisomy 18, Trisomy 21 and sex chromosome abnormalities. This test can also determine the sex of your baby. This screen is recommended for mothers at increased risk for having a baby with birth defects, such as those of advanced maternal age, have history of chromosomal abnormalities, or previous abnormal screening results. It does not screen for all potential genetic problems, only the most common ones in older women.

Diagnostic Options

If a screening test identifies an increased risk of birth defects, diagnostic tests can provide definitive information about birth defects. However, diagnostic tests carry a small risk of miscarriage, so you should discuss the risks and benefits with your provider. Most often, counseling with a genetics professional is also recommended.

Some of the most common diagnostic tests include:

  • Amniocentesis: In this procedure, a small amount of amniotic fluid is taken from the sac surrounding the baby and tested for conditions such as chromosomal abnormalities or neural tube defects.
  • Chorionic villus sampling (CVS): In chorionic villus sampling (CVS), a small sample of cells is taken from the placenta and tested for conditions such as chromosomal abnormalities and cystic fibrosis.

The decision to undergo genetic testing is a personal one. There are a number of factors to consider, such as family and medical history, personal values and risk tolerance.

“Many women choose to undergo genetic screenings because it can reduce the anxiety of the unknown,” says Dr. Corteville. “It can give you peace of mind knowing that your child has a lower-than-average risk of a genetic disorder. Many genetic disorders do not run in families and you will not know you are at higher risk without genetic screening. If a genetic anomaly is detected, we can educate parents about the potential effect on their child’s health.”

Dr. Corteville highly recommends that women considering genetic testing discuss the benefits and risks of undergoing these procedures with their prenatal care provider or a genetic counselor.

Related Links

For more information related to pregnancy, childbirth and postpartum and newborn care, visit University Hospitals OB/GYN & Women's Health pregnancy resources section. You can also check out our pregnancy handbook for a complete guide to a healthy pregnancy.