Third Trimester Scan During Pregnancy: Procedure, Tests & more

Third Trimester Scan During Pregnancy

Medically Reviewed By
Dr. Sanjana Sainani (Gynecologist/Obstetrician)
View more Gynecologist/Obstetrician Our Panel of Experts

After getting through all the hurdles, and bearing several changes in your body and your 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. If you have had several questions about scan during the third trimester, this article is for you. Here, we will talk about why it is done and what you can expect. Read on then.

What Is a Third Trimester Growth Scan?

What Is a Third Trimester Growth Scan?

It is a routine procedure that is performed to check the baby’s growth and development and to see whether any complications lie ahead. The scan is meant to measure your baby’s abdominal circumference and the size of the head and the legs. You will be advised to have a growth scan at 28 weeks and another growth scan at 32 weeks.

Why Is the Scan Done?

Here are some reasons why your doctor may ask you to get the scan done:

  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.
  1. Monitor Size and Well-Being: If you have high blood pressure or diabetes, your doctor will want to perform these tests to make sure that your baby is not having trouble growing. Sometimes there are concerns that the baby is too small or too big.
  1. Symptoms of Complications: Your doctor will need to check on the condition of your baby if you have any symptoms of complications. These could include pain, reduced foetal movement or even bleeding.
  1. Anatomy Review: Your doctor may need to double-check the state of any suspected abnormalities that may have been discovered during the ultrasound done at around 19 weeks.
  1. Placental Review: Sometimes, the placenta can show as being very low during the 19-week ultrasound. This usually corrects itself as you enter your third trimester as it gets pulled away from the cervix due to the growing uterus.
  1. Assessing Position: This becomes more important when you get closer to your due date as the doctor will need to be sure the baby is in the right position to be born.

What Will the Doctor Examine During the Scan?

The scans during the third trimester will always be done based on your own medical history and on 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 the length of the leg are what will be looked at and measured against the 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. Baby’s Heart Rate and Rhythm

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

4. Position of Placenta

The scan helps understand the position of the placenta. Conditions like placenta praevia, which is 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 be lying 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 which shows on the 50th percentile is considered to be the average size. Anything lower than the 10th percentile is a small baby, and if the percentile is above 90, it is a big baby.

8. Blood Flow in the Umbilical Cord

The measurements of the baby’s blood flow in the umbilical cord can be made using something called Doppler studies. These are very helpful in determining the well-being and health of your baby. For those babies that are not developing properly, there will be a change in the blood flow, and this is what the doctors monitor as they will be able to assess if the baby needs to be delivered early or not.

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), 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 their location noted by the doctor. Fibroid can cause pain, placental abruption and preterm delivery. Therefore, knowing the location/site and size of fibroid is very important in the third trimester. Also, this information is important for the gynaecologist if the patient ends up requiring a cesarean section because bleeding can be more than average in 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 not true. It gets much harder to see the baby, and most often, the baby will be looked at in parts. However, it is very much possible to get some beautiful and clear pictures of your little one while he is still in the womb.

There are a few things that 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 present 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 their hopes high when they walk in to get 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 also won’t be able to help you confirm the date.

Is Third Trimester Scan Safe?

Though these scans 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.


The expectant mothers who have been prescribed a third-trimester scan have to get a transabdominal ultrasound, where the scan is done through the abdomen, using a clear gel and probe. But, that’s not all. You need to know some more things that are frequently highlighted during ultrasounds. These frequently asked questions should help you.

1. Do I Need a Full Bladder for Third-Trimester Ultrasound?

A partially filled bladder is ideal for the transabdominal ultrasound as the images will be clearer. It should not be so full that it becomes painful. If that is the case, you will be asked to empty your bladder a bit 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 weight of the baby. 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 will then be able to stop and either move slightly on your side or change to a more upright position before you start to feel worse.

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 to you when you are asked to go in for these scans, remember that it does not always mean there is 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 be able to deal with the issues as early as possible so that you and your baby have a brighter future.

Also Read:

First Trimester Scans during Pregnancy
Pregnancy Ultrasound Scans

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