Third Trimester Ultrasound – What to Expect?

After overcoming all the hurdles and bearing several changes in your body and lifestyle, you have finally made it to the third trimester! As your due date draws closer and the time for you to hold your baby in your arms is approaching, your doctor is most likely going to ask you to get a third-trimester growth scan. Each scan makes the expectant parents nervous as well as excited. This article is for you if you have had several questions about scans during the third trimester. Here, we will discuss why third-trimester ultrasound is done and what you can expect. Read on then.

What Is a Third Trimester Growth Scan?

It is a routine procedure to check the baby’s growth and development and determine whether any complications lie ahead. The scan measures your baby’s abdominal circumference and the head and leg size. You will be advised to have a growth scan at 28 weeks and another at 32 weeks (2).

Is Third Trimester Scan Safe?

Though these ultrasounds in the third trimester of pregnancy are perfectly safe and do not have any side effects, your doctor may only advise you to get one done if he suspects something is amiss (5).

Why Is the Scan Done?

A growth scan in the third trimester is performed to obtain detailed images of the inside of the body, providing crucial information that assists in diagnosing medical conditions. Here are a few reasons to have an ultrasound in the third trimester:

1. Multiple Babies: Twins or triplets have a higher chance of developing growth problems in the womb due to space constriction. Doctors will want to ensure that all is well.
2. Monitor Size and Well-Being: If you have high blood pressure or diabetes, your doctor will want to perform these tests to ensure that your baby is not having trouble growing. Sometimes, there are concerns that the baby is too small or too big (1).
3. Symptoms of Complications: If you have any symptoms of complications, your doctor will need to check on your baby’s condition. These could include pain, reduced foetal movement, or even bleeding.
4. Anatomy Review: Your doctor may need to double-check the state of any suspected abnormalities that were discovered during the ultrasound at around 19 weeks.
5. Placental Review: Sometimes, the placenta can show as being very low during the 19-week ultrasound. As you enter your third trimester, this usually corrects itself as it gets pulled away from the cervix due to the growing uterus.
6. Assessing Position: This becomes more important as you approach your due date, as the doctor will need to be sure the baby is in the correct position to be born.

How Long Does a Third Trimester Growth Scan Take?

A third-trimester growth scan typically takes about 10 to 20 minutes. The duration can vary slightly depending on factors such as the baby’s position, the need for additional measurements, and the specific details your doctor is looking to assess. This time frame allows for thoroughly examining the baby’s growth, amniotic fluid levels, placenta, and overall well-being.

What Will the Doctor Examine During the Scan?

The scans during the third trimester of pregnancy will always be done based on your medical history and the results of your previous ultrasounds. Here are a few things that the doctor will examine during the ultrasound:

1. Baby Measurements

Usually, a baby’s measurements will depend on the parents. The baby’s head, abdominal muscles, and leg length will be examined and measured against a standard.

2. Amniotic Fluid

Although the quantity of amniotic fluid changes according to the stage of the pregnancy, there needs to be a certain amount of fluid present for your baby to grow well. This scan helps assess the level/amount of the fluid, too (3).

3. Baby’s Heart Rate and Rhythm

The average heartbeat a baby should have is about 120-180 beats per minute. Your baby’s heart rate will vary, just like in adults.

4. Position of Placenta

The scan helps understand the position of the placenta. Conditions like placenta praevia, which occurs when the placenta covers the mother’s cervix either totally or partially, can be diagnosed during this scan. Ideally, the lower end of the placenta should not lie too close to the cervix.

5. Length of Cervix

This is most important if you go into premature labour, have vaginal bleeding and are experiencing pain. In some cases, a transvaginal ultrasound will be done to see exactly what the problem is.

6. 3D Images of the Baby

Some parents request to see their babies in the womb, and now it is even better as there are ways to take 3D images of the child in the womb.

7. Size of the Baby

The estimated fetal weight (EFW) is usually compared to other fetuses of the same gestational age. An EFW that is shown on the 50th percentile is considered to be the average size. Anything lower than the 10th percentile is a small baby; if the percentile is above 90, it is a big baby.

8. Blood Flow in the Umbilical Cord

Measurements of the baby’s blood flow in the umbilical cord can be made using Doppler studies. These are very helpful in determining the well-being and health of your baby. If your baby is not developing properly, there will be a change in the blood flow, which the doctors monitor so they can assess if the baby needs to be delivered early (6).

9. Position of the Baby

There are three ways in which a baby could be positioned inside the womb. They are the cephalic position (head down), the breech position (buttocks down with the head at the top of the uterus), and the transverse position (baby is sideways, across the uterus). The doctors will pay closer attention to this as you near the end of the gestation period.

10. The Uterus

The uterus needs to be checked for any problems. For example, if a mother has uterine fibroids, they will be identified, and the doctor will note their location. Fibroid can cause pain, placental abruption and preterm delivery. Therefore, knowing the fibroid’s location/site and size is crucial in the third trimester. Also, this information is essential for the gynaecologist if the patient ends up requiring a cesarean section because bleeding can be more than average in the case of fibroids.

What Will the Baby Look Like in the Scan?

Though most think that the bigger the baby gets, the easier it is to see the images, this is untrue. It gets much harder to see the baby, and most often, the baby is looked at in parts. However, getting some beautiful and clear pictures of your little one while he is still in the womb is possible.

A few things influence how well the baby can be seen and what parts of the baby are visible. These are – the baby’s position, the mother’s abdomen, and the volume of amniotic fluids in the womb. These factors play important roles in giving you the much-awaited images of your little one through a scan in the third trimester.

What Can’t a Third Trimester Scan Reveal?

We know parents have high hopes when they walk in for a scan during the third trimester. But, the scan comes with a limitation. It cannot help you gauge the due date. Although a tentative date is calculated when the pregnancy is confirmed, it may not be accurate, and a scan during the third trimester won’t help you confirm the date.

FAQs

1. Do I need a full bladder for a third-trimester ultrasound?

A partially filled bladder is ideal for the transabdominal ultrasound, as the images will be more precise. However, it should not be so full that it becomes painful. If so, you will be asked to empty your bladder before continuing.

2. Why do women sometimes feel faint during the third-trimester ultrasound scan?

When you lie down, the vena cava at the back of your abdomen becomes compressed due to the baby’s weight. This makes you feel faint or nauseous, especially if you are carrying a large baby or more than one child. If you experience this while lying down for your ultrasound, it is always best to tell your sonographer, as you can stop and either move slightly on your side or change to a more upright position before you start to feel worse.

3. Will I need more frequent ultrasounds if complications are detected?

If complications are detected during the 3-trimester ultrasound, your healthcare provider may recommend more frequent ultrasounds to closely monitor the baby’s condition and the pregnancy’s progress. This ensures timely management of any issues that arise (4).

As babies grow in spurts, doctors often advise expectant mothers to undergo a series of scans as they enable them to compile information about the well-being of the babies’ with more accuracy. Though it may seem troubling when you are asked to go in for these scans, remember that it does not always mean a complication; most often, it is done to ensure everything is alright. Even if there is something to be worried about, it is always best to deal with the issues as early as possible so that you and your baby have a brighter future.

References/Resources:

1. THIRD TRIMESTER ULTRASOUND; Sydney Ultrasound for Women; https://www.sufw.com.au/services/pregnancy-ultrasound/third-trimester-ultrasound/

2. Alkutbi. H; Growth Scan: What should you expect?; Harley Street Ultrasound Group; https://harleystreetultrasound.com/articles/what-is-a-growth-scan/

3. Acevedo. H. G, Rahman. M. H, Moreno. M. A; Sonography 3rd Trimester and Placenta Assessment, Protocols, and Interpretation; National Library of Medicine; https://www.ncbi.nlm.nih.gov/books/NBK572062/#

4. Prenatal Tests: Third Trimester; Nemours KidsHealth; https://kidshealth.org/en/parents/tests-third-trimester.html

5. Common Tests During Pregnancy; The Johns Hopkins University; https://www.hopkinsmedicine.org/health/wellness-and-prevention/common-tests-during-pregnancy#ultrasound

6. Ultrasound during pregnancy; March of Dimes; https://www.marchofdimes.org/find-support/topics/pregnancy/ultrasound-during-pregnancy

Also Read:

Pregnancy Ultrasound Scans
Third Trimester Diet – What to Eat & What to Avoid
Common Pregnancy Problems in the Third Trimester
Things to Do and Avoid during Third Trimester of Pregnancy

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