The Pros and Cons of Growth Scans: Impact on Antenatal Care and Birth

Growth scans can be invaluable when there’s genuine clinical need - but in the UK, they’re sometimes over‑used, creating anxiety and influencing birth plans unnecessarily. We’re Vicky & Melissa from Beyond the Bump, here to help you navigate NICE’s antenatal care recommendations, understand when scans truly matter, and feel confident in your choices.

What Do NICE Guidelines Say?

According to the NICE NG201 antenatal care guideline:

• Routine scan at 18–21 weeks: Anomaly scan is standard for all pregnancies.

• Further growth scans only if indicated: Additional ultrasounds are recommended when there are specific risk factors (e.g., pre‑eclampsia, previous small‑for‑gestational‑age baby, diabetes) or worrying clinical signs (e.g., fundal height lagging).

• No routine third‑trimester scans: Low‑risk women with normal history and examinations should not undergo extra growth scans, to avoid false positives and unnecessary interventions.

"Ensure scans are offered based on clinical need, not routine practice, to reduce over‑medicalisation and anxiety." (NICE NG201)

The Pros of Growth Scans—When They’re Really Needed

1. Targeted monitoring: For pregnancies at genuine risk (e.g., hypertension, diabetes), growth scans can spot small or large babies early, informing decisions on timing and mode of birth.

2. Preventing complications: Detecting growth restriction can lead to timely interventions - additional monitoring, changes in maternal position, or planned delivery - potentially lowering stillbirth risk.

3. Reassurance in high‑risk scenarios: If you’ve experienced complications before, a scan provides tailored information and peace of mind.

   
   

The Cons of Unnecessary Scans

1. Increased anxiety: Measuring a baby who’s slightly under or over estimated can cause undue worry, and often resolves on its own as baby grows - growth scans have an inaccuracy rate of around 20% which is a significant variation. Growth scans also become less accurate towards the end of your third trimester as baby has started to engage.

2. Unneeded interventions: Over‑estimation may lead to inductions or caesareans that carry their own risks and longer recovery.

3. Resource strain: NHS services are best reserved for clinically indicated scans; private scans can be expensive without clear benefit.

   
   

Making Informed Decisions

• Discuss risk factors: At each antenatal appointment, ask your midwife about your risk profile - only then will additional scans be justified. Why is the scan needed, what benefit does it provide, and what are the risks.

• Track growth clinically: Fundal height measurements and checking how you feel often signal if further imaging is needed. See our blog on Fundal Height measurements to ensure you're fully informed.

• Ask about guidelines: If offered a private or extra scan, enquire how it aligns with NICE recommendations.

Use BRAIN for Informed Consent

Empower your decision-making by using the BRAIN approach:

• Benefits: What good might come from this scan? (e.g. early detection of growth issues)

• Risks: What could go wrong or cause worry? (e.g. false positives / inaccurate measurements leading to unnecessary interventions)

• Alternatives: What other ways can we monitor growth? (e.g. fundal height checks, doppler scans)

• Intuition: How do you feel about having the scan? Trust your instincts.

• Nothing: What if you choose to wait, do you need more time to think about your options

This ensures fully informed consent, free from pressure or anxiety and allows you to process everything in your own way before agreeing either way.

Next Steps & Resources

Growth scans are a powerful tool when used wisely. Remember:

Knowledge is power = ensure any scan you have is based on clinical guidance, not routine practice.

If this blog has got you thinking, "What else don't I know yet?", grab our free guide, You're Probably Preparing for Birth Backwards: 3 Simple Shifts That Change How Prepared You Feel for Labour.

And if you're ready to prepare more deeply, join us inside The Birth Preparation Programme. Because confidence doesn't come from having the perfect birth plan. It comes from understanding your options, knowing how to advocate for yourself, communicating your needs clearly, and feeling prepared for whatever path your pregnancy and birth take.

We help you navigate the decisions, conversations, and realities of modern maternity care, so you can approach birth feeling informed, confident, and in control of the things that matter most to you

Frequently Asked Questions About Growth Scans in Pregnancy

Are growth scans routine in the NHS?

No. According to NICE guidance, routine growth scans are not recommended for low-risk pregnancies. Most women will have a dating scan and an anomaly scan, with additional growth scans only offered if there are specific risk factors or concerns about baby's growth.

How accurate are growth scans?

Growth scans are estimates rather than exact measurements. Research suggests ultrasound estimates can vary by approximately 10–20% either way, particularly in the final weeks of pregnancy. This means a baby estimated to weigh 8lb could actually weigh significantly more or less.

Can a growth scan tell me exactly how much my baby weighs?

No. Growth scans use measurements such as head circumference, abdominal circumference, and femur length to estimate weight. They cannot provide an exact birth weight.

Why have I been offered a growth scan?

You may be offered a growth scan if there are concerns about your baby's growth, your fundal height measurements differ from expected, or you have certain risk factors such as:

• High blood pressure

• Diabetes

• Previous small baby

• Previous stillbirth

• Multiple pregnancy

• Concerns about placental function

What happens if my baby measures small on a growth scan?

If a growth scan suggests your baby is smaller than expected, your maternity team may recommend additional monitoring. This could include repeat growth scans, Doppler scans to assess blood flow through the placenta, or discussions about birth timing if concerns continue.

What happens if my baby measures large on a growth scan?

A growth scan estimate alone does not automatically mean induction or caesarean birth is needed. Your healthcare team should discuss the full clinical picture, including your health, previous births, and the limitations of scan accuracy before making recommendations.

Can growth scans be wrong?

Yes. Growth scans can both underestimate and overestimate a baby's size. This is one reason NICE does not recommend routine third-trimester scans for low-risk pregnancies.

Do growth scans increase the risk of induction?

Research suggests that suspected concerns about baby's size can sometimes lead to increased intervention, including induction of labour. It's important to understand whether recommendations are based on actual concerns or estimated measurements alone.

Are private growth scans worth it?

For low-risk pregnancies without clinical concerns, there is limited evidence that additional private growth scans improve outcomes. However, some parents choose them for reassurance. It's worth considering the benefits, limitations, costs, and potential for unnecessary anxiety before booking.

Can I decline a growth scan?

Yes. Like all maternity care, growth scans are offered, not mandatory. You have the right to receive information about the benefits, risks, and alternatives before making a decision that feels right for you.

What are the alternatives to growth scans?

Depending on your circumstances, alternatives may include:

• Fundal height measurements

• Monitoring your baby's movements

• Clinical assessment by your midwife or obstetrician

• Doppler monitoring when clinically indicated

Do growth scans become less accurate at the end of pregnancy?

Yes. As pregnancy progresses, especially after 36 weeks, estimating a baby's size becomes more difficult. Factors such as baby's position, engagement in the pelvis, and reduced space can affect measurement accuracy.

Can a growth scan predict birth weight?

Not reliably. While growth scans can provide an estimate, they cannot accurately predict exactly how much your baby will weigh at birth.

Does a big baby mean I need an induction?

Not necessarily. NICE guidance does not recommend routine induction solely because a baby is suspected to be large. Decisions should be individualised and based on the whole clinical picture.

Does a small baby always mean there is a problem?

No. Some babies are constitutionally small and perfectly healthy. Growth scans help identify babies who may need additional monitoring, but a smaller estimated size does not automatically mean something is wrong.

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