Third-Trimester Screening Tests


As you enter the final stage of your pregnancy, the third trimester brings a mix of anticipation and diligent preparation. At May-Grant OB-GYN, servicing Lancaster, PA, we know that screening tests during this stage can prompt many questions. This blog aims to guide you through the maze of third-trimester screening tests, empowering you with knowledge for this crucial stage of your pregnancy journey.

The Importance of Third-Trimester Screening Tests

Screening tests in the third trimester are primarily geared toward ensuring your and your baby’s health and safety. They help identify potential health issues that may require special care or intervention. This monitoring period provides essential insight into how your pregnancy progresses and prepares you for what to expect during delivery.

  • Health Status Check: The tests assess your health, checking for conditions like gestational diabetes or preeclampsia, which could impact your pregnancy.
  • Baby’s Development: They monitor your baby’s development and well-being, keeping an eye on their growth, movement, and overall health.
  • Preparation for Delivery: The tests also help make informed decisions about your delivery process, including the delivery method and any need for special care for your baby after birth.

Common Third-Trimester Screening Tests

The third trimester is a period of close monitoring. Here’s an overview of some common screening tests you might encounter during this stage of your pregnancy.

Glucose Screening

While glucose screening is typically performed in the second trimester, if you tested negative earlier and have risk factors for gestational diabetes, your healthcare provider might opt for another round of testing in the third trimester.

  • What It Involves: You’ll consume a sweet liquid, and your blood will be drawn after a specified time to check your body’s response to sugar.

Group B Strep (GBS) Test

GBS is a bacteria often found in the digestive tract. It’s harmless for adults but can cause serious infections in newborns.

  • What It Involves: A swab is taken from your vagina and rectum for testing. If positive, antibiotics can be given during labor to protect the baby.

Biophysical Profile (BPP)

A BPP combines an ultrasound with a non-stress test to check your baby’s overall well-being.

  • What It Involves: The ultrasound measures your baby’s movement, muscle tone, and breathing, along with the amount of amniotic fluid, while the non-stress test assesses your baby’s heart rate.

Non-Stress Test

This test monitors your baby’s heartbeat and reaction to their movements.

  • What It Involves: Two monitors are placed on your abdomen—one tracks your baby’s heartbeat, and the other tracks contractions.


While not always routine, an ultrasound might be performed in the third trimester to check your baby’s growth and the location of the placenta or in case of any concerns.

  • What It Involves: A device that uses sound waves to create images of your baby in the womb is moved over your abdomen.

Understanding Your Results

Interpreting test results can be complex. At May-Grant OB-GYN, we ensure that we walk you through the findings, helping you understand what they mean for you and your baby. Remember, an abnormal result doesn’t necessarily imply a problem—it often leads to further tests for a clearer understanding.

Preparing for Your Tests

As you approach these tests, here are a few tips to help you prepare:

  • Know What to Expect: Familiarize yourself with what each test involves. This will reduce anxiety and help you make necessary arrangements, like adjusting your meal schedule for a fasting test.
  • Communicate Openly: Don’t hesitate to voice your concerns or queries to your healthcare provider. Their goal is to ensure you feel comfortable and informed.
  • Maintain Records: Keep track of your test dates and results. This can help you stay organized and make sharing information with other healthcare professionals involved in your care easier.

Embrace the Journey

Third-trimester screenings play a crucial role in your and your baby’s health and well-being. While these tests may seem daunting, remember that they’re steps on your journey toward meeting your little one. At May-Grant OB-GYN, we are committed to guiding you through this process, providing you with comprehensive care and support.


  1. American Pregnancy Association. (2020). Third Trimester Tests During Pregnancy.
  2. Mayo Clinic. (2019). Third-trimester pregnancy: What to expect.
  3. American College of Obstetricians and Gynecologists. (2020). Routine Tests in Pregnancy.
The Promise We Make to Our Patients
The Promise We Make to Our Patients

The overarching mission at May-Grant Obstetrics & Gynecology is to help women of all ages live a healthy life. From general gynecological services to helping you through navigating pregnancy and menopause, our team of certified physicians, midwives, and certified registered nurse practitioners pride themselves on being leaders in women’s healthcare throughout Lancaster, PA.

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"Having been a patient of May-Grant for over 2 years, I can proudly say that all of their providers are top-notch. They really listen and always asks the right questions. The registered nurses and midwives are so personable as well. I couldn't ask to be working alongside a better team..."
February, 2023
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