Expert / 7 June, 2021 / Dr Ellie Rayner

Growth Scans In Pregnancy: What Are They And Why Are They Performed?

A growth scan is an ultrasound scan that is normally performed in the third trimester of pregnancy and checks how well your baby is growing and can be used as a tool to assess their overall wellbeing.

If you are having a low-risk, straightforward pregnancy, you will be offered two ultrasound scans as part of your NHS care pathway. A first scan between 10 to 14 weeks of pregnancy often called a dating scan. This scan aims to estimate your date of birth or ‘due date’ based on the measurements of your baby. The second scan you will be offered is usually performed between 18 and 21 weeks of pregnancy and looks in detail at the anatomy of your baby, checking for eleven rare physical conditions related to your baby’s development.

Depending on your circumstances, you may be offered additional growth scans by your midwife or Obstetrician to monitor your baby’s growth and wellbeing during your pregnancy if they feel you are at risk of developing complications. The most common complication growth scans are looking for is if you are at increased risk of having a small baby (estimated weight less than the 10th centile).

At your booking appointment, your midwife will take a detailed medical, social and family history, including asking for information on any previous pregnancies you have had and your baby’s previous birthweights to assess whether you should be recommended additional scans or not. In most circumstances, if you meet the criteria, this will include 2 or 3 additional scans spread throughout your third trimester (from 28 weeks onwards). Additionally, some hospitals offer all parents a single additional growth scan at around 36 weeks of pregnancy as routine and your local maternity unit should arrange this for you if this is the case in your area.

Why might I be offered a growth scan(s)?

There are two main reasons you might be offered an additional growth scan(s).

1) Your medical, social or obstetric history:

If you have certain medical conditions, such as having diabetes or high blood pressure, if you smoke or over-exercise, if you have had a previous baby less than the 5th centile. Also, if measuring your bump (symphysis fundal height) with a tape measure, as your midwife will be doing routinely at your antenatal appointments, may not be reliable in your situation, such as your BMI being is more than 40 or if you have fibroids, you may be recommended growth scans from the outset of your pregnancy.

2) If, during your pregnancy, any concerns arise that may affect your baby’s development or wellbeing, such as recurrent bleeding, decreased fetal movements, pregnancy-induced high blood pressure or preeclampsia. You may also be referred for an additional scan(s) if when your midwife measures your bump, the measurement is different to expected for your baby’s gestational age.

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What are they looking for during a Growth Scan?

During a growth scan, the healthcare professional will take several different measurements of your baby to assess their growth and wellbeing.

They will:

– Check your baby’s heartbeat and observe for baby movements
– Measure their head circumference (HC)
– Measure waist circumference (abdominal circumference, AC)
– Measure thigh bone length (femur length, FL)
– Measure the volume of amniotic fluid around your baby
– Measure the blood flow through the umbilical cord.
– Check the position your baby is lying and the location of your placenta

They will then plot all measurements onto charts to assess your baby’s size and allow comparison of the growth of your baby over time and finally summarise the results into a report for your healthcare team.

When will I know the result?

In the majority of cases, growth scans are normal and reassuring and you will be given the results and the opportunity to discuss the scan on the same day with a healthcare professional and make a plan for if any further scans are indicated and when these will be.

If your baby is found to be small, or if there are any other findings on the scan that are outside the normal range you will be referred to a healthcare professional to discuss the scan findings in full, as soon as possible. They will explain what the findings mean and may recommend increasing the frequency of monitoring or offer additional tests or assessments to monitor the wellbeing of your baby.

What are the risks and benefits of having Growth Scans?

Ultrasound scans have been used for many years during pregnancy and there are no known risks to you or your baby from having additional growth scans. The benefit of having a growth scan if you are offered one is to ensure your baby is growing as expected and to enable healthcare professionals to identity any problems as soon as possible so they can reduce the chance of serious complications.

As with all aspects of maternity care, there will be a medical rationale for why you are recommended additional scans and this should be explained to you in full to gain your consent beforehand, however, it remains your choice whether you choose to accept these or not. If you would like any more information on growth scans or having a small baby the Royal College of Obstetricians and Gynaecologists has a dedicated patient information leaflet entitled: Having a Small Baby on their website.

Dr Ellie Rayner, Obstetrician and Gynaecologist, Antenatal and Hypnobirthing Teacher and founder of The Maternity Collective.

Dr Ellie Rayner is a practicing Obstetrician and Gynaecologist and founder of The Maternity Collective. She is the only Obstetrician to offer private and group, expert-led Antenatal and Hypnobirthing Classes both Online and face-to-face. She is passionate about providing parent-centred, evidence-based care for all pregnancies and supports all methods of birth.

Follow Dr Ellie Rayner @maternitymedic for the latest evidence-based information on pregnancy, birth and women’s health issues.

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