PregnancyHealth and Safety37 Week Ultrasound: What To Expect At The Last Ultrasound Scan

37 Week Ultrasound: What To Expect At The Last Ultrasound Scan

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Let the countdown begin! At 36-38 weeks, you’re in your ninth month of pregnancy and you are almost at the finish line. You’ll likely have one final ultrasound to check on things prior to labor. Done around 37 weeks, during this ultrasound your doctor will take measurements that estimate your baby’s weight and the amount of amniotic fluid in your belly. They’ll also double check baby’s positioning to confirm whether he or she is ‘head down’ or ‘breech’ (legs down).

You might find yourself with a burst of energy at this stage—the ‘nesting’ instinct really kicks in as you are busy grocery shopping and putting the final touches on the nursery. Or, you might be totally exhausted, and that’s normal too!

Your baby at 37 weeks

A 37-week-old baby has almost reached their birth weight. An average baby of this gestational age is about 6.5-7 pounds and around 19 inches long. He or she is about the size of a cantaloupe or a head of lettuce.

Your little one is very busy in the womb getting ready to be earth-side—they are practicing sucking and you may even catch them with their thumb in their mouth. They are also using their little hands to practice grasping and might be grabbing onto their own nose, feet, or other body parts.

In order to keep warm once out of the womb, they are adding layers of fat; get ready for those edible baby rolls!

By now, your baby can recognize your voice. Keep talking and singing to your baby—the same voice will soothe him or her during middle-of-the-night wakings in a few weeks. You might also want to read to your baby whilst still in your womb.

Noticing a difference in fetal movement? In late pregnancy, you may notice a change in the way it feels when your baby moves. Your uterus is becoming increasingly cramped and, as a result, your baby might be rolling and wriggling more than karate chopping, like before. Still, you should feel your baby moving regularly. Speak with your doctor about whether they recommend kick counts and how often.

Braxton Hicks Contractions

You might be noticing your uterus tightening every once in a while. Unless this is happening at regular intervals, it’s probably something called Braxton Hicks Contractions, which is your body’s way of practicing for the real deal. These practice contractions may happen more when you are dehydrated or more active than usual.

Don’t worry, they’re totally normal and can start as early as 16 weeks!

The Ultrasound Scan

Just like with your Anatomy Scan, the uterus and baby are big enough now that this ultrasound can be done abdominally versus transvaginally. Once again, your doctor will apply gel and a rounded transducer to examine your abdomen.

Estimated Fetal Weight (EFW)

Sometimes called the ‘fetal growth scan’, this ultrasound will provide measurements that calculate your baby’s estimated weight before birth. By measuring things like your baby’s head circumference, abdominal circumference, and femur length, your doctor will be able to estimate how many pounds your baby currently is.

Amniotic Fluid Index (AFI)

The Amniotic Fluid Index, commonly called AFI, is found by dividing the uterus into four imaginary quadrants to measure the amount of amniotic fluid. Ideally, you’ll have between five and 25 centimeters of fluid in total.

  • A measurement of fewer than five centimeters indicates oligohydramnios, or low amniotic fluid.
  • A measurement of greater than 25 centimeters indicates polyhydramnios, or too much amniotic fluid.

If you’re found to have too much or too little amniotic fluid, your healthcare provider will monitor the rest of your pregnancy very carefully to make sure your baby remains safe and healthy. In some cases, your doctor will want to induce labor early or perform a C-Section to get baby out ASAP.

What else can you expect from this visit?

Group B Strep (GBS)

Around 36 weeks, your doctor will do a test to look for ‘Group B Strep’, or Group B Streptococcus bacteria. While these bacteria are commonly found as normal vaginal flora, they can cause neonatal sepsis in newborns.

Because your baby is at risk of contracting bacteria from you as they pass through the vaginal canal, if you test positive for Group B Strep, your doctor will want to treat you with intravenous antibiotics during labor. According to the CDC, about 1 in 4 women will test positive for Group B Strep.

The test is performed as a quick swab of your pelvic area. Your doctor will use a long cotton swab to take a sample from your vaginal cavity and anus. That swab will then be sent to the lab to test for the bacteria.

Having a scheduled Cesarean Section? You can probably skip the GBS screening, but be sure to check with your doctor.

Cervix Check

While completely optional, some doctors begin offering routine cervical exams around 36 weeks.

The cervix is the narrow opening at the bottom of the uterus that connects to the vagina and forms the birth canal through which your baby will pass during vaginal birth. As labor nears, the cervix begins to dilate, or open, and become effaced, meaning it stretches and thins.

In the final weeks before labor, your doctor might want to check your cervix to see what kind of progression your body is making as your due date nears.

The efficacy of cervix checks is sometimes questioned because they’re not necessarily an indication of when labor will start – some women walk around with a dilated cervix for weeks, while others are completely ‘closed’ one day and go into labor the next. Still, cervix checks can provide helpful information to both you and your doctor leading up to the birth of your baby.

Nonstress Test (NST)

An NST is a non-invasive test that involves attaching two monitors to your belly for 20-30 minutes. These monitors track contractions, fetal movement, and fetal heart rate.

Depending on your risk profile, your doctor might want you to have weekly Nonstress Tests in the final weeks of pregnancy to ensure your baby is doing well in the womb.

What’s next?

It’s almost time to meet your baby! These final weeks are a good time to ensure you’re as ready as possible for the arrival of your little one:

  • Pack your hospital bag. Make sure you have outfits for your new bundle of joy, comfy pajamas or a robe, slippers, and a phone charger. Take a look at our guide to what to pack.
  • Choose your pediatrician. You may even want to schedule a meeting with a few potential options to ensure the right fit.
  • Create a birth plan. If you haven’t done so already, now is a good time to think about your preferences during birth. You can express desires like keeping the lights low during labor, keeping noise to a minimum, and whether you want your partner to cut the umbilical cord once the baby is born. Take a look at our range of visual birth plans.

Read More of Our Series on Ultrasound Scans

The Viability Check Ultrasound Scan

The 10 Week Ultrasound Scan

The 20 Week Anatomy Scan

Written by

Abigail Purcell, RN
Abigail Purcell, RN
Abigail is one of our expert writers and is a BSN, RN (Registered Nurse) with a wide range of experience. She has worked in Public Health, Medical-Surgical nursing, and, most recently, Paediatrics and Women’s Health. Her true passion is serving mothers and families by helping them navigate their healthcare. As a nurse writer, Abby enjoys being able to empower patients on a larger scale, using evidence-based information that is easy to access and understand.


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