Third Trimester Scan During Pregnancy

A pregnant woman getting an ultrasound done

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After getting through all the hurdles and bearing with so many changes in your body and lifestyle because of your pregnancy, 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 go in for a third-trimester growth scan.

What is a Third Trimester Growth Scan?

A pregnant woman getting an ultrasound done

This 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, head and legs. You will be advised to have a growth scan at 28 weeks and another growth scan at 32 weeks.

Why is this Scan Done?

Here are some reasons your doctor may ask you to get these scans done:

  1. Multiple Babies: Twins or triplets have a higher chance of developing growth problems in the womb due to there being so little space. 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 fetal 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 the closer you get 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 based 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:

There needs to be a certain amount present in order for your baby to grow well. There are wide ranges of these fluids during pregnancy, though it will change according to the stage of pregnancy.

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 for adults.

4. Position Of Placenta:

The inner end of the placenta should not be lying too close to the cervix, a phenomenon called “placenta praevia.”

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 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 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 Umbilical Cord:

The measurements of the baby’s blood flow in the umbilical cord are measured 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 Baby:

There are three ways in which your baby could be positioned inside the womb. These are the cephalic position (Heads down), breech position (buttocks down, 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 closer to 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.

What will the Baby Look Like in the Scan?

Though most think that the bigger the baby gets, the easier it is to see, this could not be further from the truth. It gets much harder to see the baby, and most often the baby will be looked at in parts.
It is very much possible to get some beautiful and clear pictures of your baby 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. The baby’s position, the mother’s abdomen and the volume of amniotic fluids present in the womb all play important roles here.

What 3rd Trimester Scan Can’t Reveal?

Here are a few things 3rd-trimester scans cannot reveal:

  • Baby Weight: The bigger the baby, the harder it becomes to assess all the information wanted about its growth. The baby’s weight is something the doctor cannot make out as sometimes the positioning will hinder the ability to measure the head, abdomen and legs of the baby.
  • Blood Source: If there is any bleeding, the scans won’t be able to tell where it is coming from.
  • Due Date: Your due date should already have been established before 20 weeks of gestation as babies become unique in size and shape.

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.


In the third trimester, the ultrasound is done using the transabdominal ultrasound, where the scan is done through the abdomen, using a clear gel and probe. Another way of monitoring your baby’s growth and progress is through the transvaginal ultrasound. This involves the probe lying in the vagina. Your permission is always required before a transvaginal ultrasound is performed.

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 this is the case, you will be asked to empty your bladder a bit before continuing. If the transvaginal ultrasound is needed, you will be asked to empty your bladder before starting.

2. Why Do Women Sometimes Feel Faint during 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 cause you to become nauseous and faint, especially if you are carrying a large baby or carrying 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 to lying 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 you to undergo a series of scans rather than just the one scan as this will enable them to compile information about your baby’s well-being 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 definitely going to be a complication; most often it is done to ensure that all is well. 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 will have a brighter future.

Also Read:

First Trimester Scans during Pregnancy
Pregnancy Ultrasound Scans