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

Growth scans are ultrasound examinations carried out during the third trimester of pregnancy to assess how your baby is growing and to check their overall wellbeing as pregnancy progresses. Unlike routine scans earlier in pregnancy, growth scans are offered when there is a clinical reason to look more closely at growth, placental function, or amniotic fluid levels.

At Central Health London, growth scans are used as a supportive and informative tool. They help guide care, provide reassurance when growth is on track, and allow early intervention if concerns arise. Being offered a growth scan does not automatically mean something is wrong. In many cases, it is simply a way to ensure your pregnancy continues safely.

What Is a Growth Scan?

A growth scan is a detailed ultrasound performed in the third trimester to assess fetal size, growth patterns, and the environment supporting your baby in the womb. It provides more information than routine fundal height measurements and allows clinicians to track development over time.

Growth scans focus not just on your baby’s size, but also on how well the placenta is working and whether fluid levels are appropriate. This broader picture helps clinicians make informed decisions about monitoring and birth planning.

When Are Growth Scans Carried Out?

Growth scans are most commonly performed during the later stages of pregnancy, often at:

• 28 to 32 weeks

• 32 to 36 weeks
  

Some women may be offered more frequent scans if closer monitoring is needed. The timing and frequency are always based on your individual circumstances, medical history, and pregnancy findings. Your obstetrician or midwife will explain why a scan is recommended and what information it is intended to provide.

What Does a Growth Scan Check?

Growth scans assess several key aspects of your baby’s development and wellbeing.

1. Estimated Fetal Weight

Measurements of the baby’s head, abdomen, and femur are used to estimate fetal weight. This estimate is then plotted on national growth charts to understand how your baby’s size compares with expected ranges for gestational age.

2. Baby’s Growth Pattern

Rather than focusing on a single measurement, clinicians look at growth trends over time. Babies may be identified as:

• Growing appropriately for gestational age

• Small for gestational age

• Large for gestational age
  

Understanding growth patterns helps guide monitoring and care decisions.

3. Amniotic Fluid Levels

The amount of amniotic fluid surrounding your baby is assessed to ensure it falls within a healthy range. Fluid levels that are too low or too high can provide important information about placental function and fetal wellbeing.

4. Placental Health and Position

The placenta is reviewed to ensure it is functioning effectively and is positioned safely away from the cervix. Placental assessment helps determine how well oxygen and nutrients are being delivered to your baby.

5. Blood Flow and Doppler Studies

Where needed, Doppler ultrasound is used to assess blood flow in the umbilical cord or specific fetal blood vessels. These measurements provide insight into how well the placenta is supporting your baby, particularly if growth concerns are suspected.

Why You Might Be Offered a Growth Scan

Not every pregnancy requires growth scans, but they are recommended when certain risk factors or clinical findings are present. These may include:

• Concerns about your baby’s size

• Differences between fundal height measurements and gestational age

• Maternal medical conditions such as diabetes or hypertension

• A previous pregnancy affected by growth restriction

• Concerns about amniotic fluid levels

• Multiple pregnancy

• A low-lying placenta earlier in pregnancy

• Reduced fetal movements
  

Your clinician will discuss the reason for recommending a growth scan and how the results will inform your care.

What Happens During a Growth Scan?

A growth scan is similar in experience to earlier ultrasound examinations. A sonographer or fetal medicine specialist applies gel to your abdomen and uses an ultrasound probe to take measurements and assess structures.

The scan is painless, non-invasive, and typically lasts around 20 to 30 minutes. You will usually be given information about the findings either during the scan or shortly afterward, including how your baby’s estimated weight sits on the growth chart.

What Happens if the Scan Shows a Concern?

If a growth scan suggests that your baby is growing more slowly or more quickly than expected, or if there are concerns about fluid levels or placental function, further monitoring may be recommended.

This can include:

• Repeat growth scans

• Doppler monitoring

• Additional antenatal appointments

• Adjustments to your pregnancy care plan

• Discussion of timing or mode of birth in some circumstances
  

Your obstetric team will talk you through the findings and ensure you understand the next steps. Care is always tailored to your individual situation.

Are Growth Scans Safe?

Yes. Growth scans use ultrasound technology, which is non-invasive and does not involve radiation. Ultrasound is considered safe when performed by trained healthcare professionals and is widely used throughout pregnancy to monitor fetal wellbeing.

Frequently Asked Questions About Growth Scans in the Third Trimester

What is a growth scan in pregnancy?

A growth scan is an ultrasound examination carried out during the third trimester to assess your baby’s size, growth pattern, and overall wellbeing. It looks at estimated fetal weight, amniotic fluid levels, placental function, and sometimes blood flow. Growth scans help clinicians understand how your baby is developing as pregnancy progresses.

When is a growth scan usually done?

Growth scans are most commonly performed between 28 and 36 weeks of pregnancy. The exact timing depends on your medical history, pregnancy findings, and any risk factors present. Some women may be offered more than one scan to monitor growth trends over time rather than relying on a single measurement.

Why might I be offered a growth scan?

You may be offered a growth scan if there are concerns about your baby’s size, differences in fundal height measurements, reduced fetal movements, or maternal medical conditions such as diabetes or hypertension. A history of growth issues in previous pregnancies or a multiple pregnancy may also prompt closer monitoring.

What does a growth scan actually measure?

A growth scan measures your baby’s head, abdomen, and thigh bone to estimate weight. It also assesses amniotic fluid levels, placental position and function, and sometimes blood flow using Doppler studies. Together, these measurements provide a detailed picture of how well your baby is being supported in the womb.

How accurate are growth scans?

Growth scans provide estimates rather than exact measurements. While they are useful for identifying growth patterns and trends, estimated fetal weight can vary. Clinicians interpret results alongside clinical findings and repeat measurements when necessary, rather than relying on a single scan alone.

How long does a growth scan take?

Most growth scans take around 20 to 30 minutes. The length of the scan can vary depending on your baby’s position and whether additional assessments, such as Doppler studies, are required. You will usually receive feedback on the findings during or shortly after the scan.

What happens if my baby is measuring small?

If your baby is identified as small for gestational age, your clinician may recommend closer monitoring. This can include repeat growth scans, Doppler assessments, and additional antenatal appointments. Many babies who measure small are healthy, but monitoring ensures any concerns are identified early.

What happens if my baby is measuring large?

If your baby is measuring larger than expected, your care team may discuss additional monitoring and how this could affect birth planning. This does not automatically mean intervention is required, but it allows time to plan safely and consider all options based on your individual circumstances.

Do growth scans affect birth planning?

Growth scan findings can inform discussions about timing and mode of birth, particularly if there are concerns about growth, placental function, or maternal health. These discussions happen gradually and collaboratively, ensuring you understand your options and feel involved in decision-making.

Are growth scans safe for my baby?

Yes. Growth scans use ultrasound, which is considered safe in pregnancy when performed by trained professionals. They are widely used to monitor fetal wellbeing and provide valuable information without exposing you or your baby to harm.

Do all pregnancies need growth scans?

No. Many pregnancies progress normally without the need for growth scans. They are offered when there is a clinical reason to monitor growth more closely, based on individual risk factors or findings during routine care.

When should I seek advice after a growth scan?

You should seek advice if you have concerns following a scan, experience reduced fetal movements, or feel unsure about the results. Your care team is there to explain findings and support you, and it is always appropriate to ask questions or request clarification.