Growth Scans in the Third Trimester – Why They’re Done and What They Show

What Is a Growth Scan?

A growth scan is an ultrasound performed during the third trimester to assess how your baby is growing and to check their wellbeing as your pregnancy progresses. Unlike your routine scans earlier in pregnancy, growth scans are carried out only when clinically indicated – for example, if there are concerns about the baby’s size, your health, or other factors affecting pregnancy.

When Are Growth Scans Carried Out?

Growth scans are most commonly performed at:

• 28–32 weeks

• 32–36 weeks

• And more frequently if closer monitoring is needed

Your obstetrician or midwife will recommend the timing based on your individual circumstances.

What Does a Growth Scan Check?

Growth scans provide a detailed picture of your baby’s development. They typically include:

1. Estimated Fetal Weight (EFW)

Measurements of the baby’s head, abdomen and femur are used to estimate weight and compare it with national growth charts.

2. Baby’s Growth Pattern

Your clinician looks for growth that is consistent and appropriate for gestational age, identifying whether the baby is:

• Growing normally

• Small for gestational age (SGA)

• Large for gestational age (LGA)

3. Amniotic Fluid Levels

Scans assess whether the fluid levels are normal, low (oligohydramnios) or high (polyhydramnios).

4. Placental Health and Position

The placenta is checked to ensure it is functioning well and not obstructing the cervix.

5. Blood Flow (Doppler Studies)

Where needed, Doppler ultrasound is used to assess the blood flow in the umbilical cord or baby’s blood vessels, offering insight into how well the baby is being supported by the placenta.

Why You Might Be Offered a Growth Scan

Not every pregnancy needs late scans, but they are recommended when there are risk factors such as:

• Concerns about the baby’s size

• Reduced fundal height measurements

• Maternal medical conditions (e.g., hypertension, diabetes)

• Previous baby with growth restriction

• Concerns about amniotic fluid levels

• Twins or multiple pregnancy

• Low-lying placenta earlier in pregnancy

• Reduced fetal movements

Your clinician will discuss why a growth scan may be helpful in your pregnancy.

What Happens During the Scan?

A growth scan is similar to your earlier ultrasound examinations. A sonographer or fetal medicine specialist measures the baby, checks organ structures and reviews the placenta and fluid. The scan is painless, safe and usually takes around 20–30 minutes.

You will receive clear information during or after the scan, including the estimated fetal weight and how this sits on the growth chart.

What Happens if the Scan Shows a Concern?

If the scan suggests that the baby is growing too slowly or too quickly, or if there are issues with fluid levels or placental function, your clinician may recommend:

• Repeat growth scans

• Doppler monitoring

• Additional antenatal checks

• Adjustments to your pregnancy care plan

• Early delivery in some circumstances

Your obstetric team will guide you through the next steps and ensure you have the right support.

Are Growth Scans Safe?

Yes. As with all pregnancy ultrasound examinations, growth scans are non-invasive and considered safe when performed by trained professionals.

FAQs for Growth Scans in the Third Trimester

What is a growth scan in pregnancy?

A growth scan is an ultrasound examination carried out in the third trimester to assess your baby’s size, growth pattern and overall wellbeing.

When is a growth scan usually done?

Growth scans are typically performed between 28 and 36 weeks, with the exact timing depending on your individual circumstances and your clinician’s recommendation.

Why might I be offered a growth scan?

You may be offered a growth scan if there are concerns about your baby’s size, a discrepancy in fundal height measurements, maternal medical conditions such as hypertension or diabetes, reduced fetal movements, or a history of growth concerns in previous pregnancies.

What does a growth scan check?

The scan assesses estimated fetal weight, your baby’s growth trend, amniotic fluid levels, placental health and, where appropriate, blood flow using Doppler studies.

How long does a growth scan take?

Most growth scans take around 20–30 minutes, depending on the baby’s position and whether additional Doppler assessments are needed.

What happens if the scan shows my baby is too small or too big?

If there are growth concerns, your clinician may recommend further monitoring, additional scans, Doppler assessments or adjustments to your antenatal care plan. In some cases, early delivery may be discussed.

Are growth scans safe?

Yes. Growth scans use ultrasound, which is non-invasive and considered safe when performed by trained healthcare professionals.

Do all pregnant women need a growth scan?

No. Growth scans are performed when there is a clinical reason to monitor your baby’s development more closely.