Third-Trimester Ultrasound: A Final Check on Your Baby

At 36 weeks, exam gauges baby’s size and position

Nicole and family

By week 36 of pregnancy, the wait is almost over. Soon, you’ll meet your baby. For some parents — especially older moms-to-be — technology helps doctors take one last look before delivery.

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Nicole Herbst, who at age 39 was expecting her first child, had a third trimester ultrasound. Not only did it put her mind at ease, but it also allowed her to see her baby’s face for the first time.

“My technologist looked at the baby’s heart, took measurements and checked her position,” Ms. Herbst says. “She then generated some 3-D images and we saw our baby’s face. Her eyes were closed — she might have been sleeping — and we saw her breathing. Thinking back to the photo they gave us, it pretty much looked like her when she was born.”

Ultrasound’s role during pregnancy

For more than 30 years, medical professionals have used ultrasounds to view a baby’s development. The technology uses high-frequency sound waves, which are recorded and changed into video or photographic images of your baby. Ultrasounds are considered safe. They don’t expose your baby to radiation, making them safer than X-rays.

“We use third trimester ultrasounds when we want to make sure everything is going as planned with the mom and baby,” says maternal fetal medicine specialist Abdelaziz Saleh, MD. “A 36-week ultrasound is one of the prenatal tests we might want to use, although getting one that far into the pregnancy isn’t the standard. It’s usually something we do when the woman is of advanced maternal age or we want to double check the baby.”

The number of ultrasounds a pregnant woman receives varies, depending on her age, health history, her doctor and the purpose of the test. At each stage, doctors may be checking a different thing:

  • First trimester ultrasounds help determine the baby’s gestational age.
  • In the second trimester, multiple babies can be confirmed. During this period, at 20 weeks or so, the baby’s sex can usually be determined.
  • Third trimester ultrasounds view the baby’s size, position and movements and check for any complications.

What to expect

Doctors use ultrasounds as diagnostic procedures to view the baby’s heart, blood vessels, kidneys, liver and other organs. The tests do not cause any discomfort.

Here’s what you can expect:

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  • While the mom-to-be reclines on an exam table, the technician applies water-soluble gel to her abdomen.
  • The technician moves a small device called a transducer over the abdomen. The transducer sends high-frequency sound waves into the body, which reflect off internal structures, including your baby. The transducer receives the sound waves or echoes that reflect back and transforms them into pictures on a screen. These pictures can be printed out.
  • There are different kinds of ultrasounds, depending on what your doctor wants to check.

Added confidence and reassurance

Ms. Herbst, who is now 40, first had an ultrasound at 18 weeks into her pregnancy.

When her maternal-fetal specialist sent her for the 36-week ultrasound, Ms. Herbst considered it part of the plan.

“For my husband, Rob, and me, it was reassuring to know that our baby was growing and on target to be a healthy-weight baby,” she said. “When we saw her, we knew things were looking good.”

In March, 2014, the Herbsts joyfully welcomed their baby girl, who was born at Fairview Hospital.

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