Growth Scan in Pregnancy: Your Complete Guide
A growth scan is an ultrasound offered in the second or third trimester to check that your baby is growing as expected. Some are arranged routinely by the NHS, while others are recommended if your care team has any concerns or if you choose to book one privately. This complete guide explains what a growth scan is, when it is offered, what it measures, how to understand the results, and what happens if your baby is measuring small or large.
What Is a Growth Scan?
A growth scan is a detailed ultrasound that measures your baby's size and estimates their weight. The sonographer takes measurements of the head, abdomen, and thigh bone, and uses these to calculate an Estimated Fetal Weight. They may also check the amniotic fluid levels and the blood flow in the umbilical cord, known as Doppler measurements, to assess how well the placenta is supporting the baby.
When Are Growth Scans Offered?
The NHS does not offer a routine growth scan to everyone, but you may be offered one if your midwife or doctor has any concerns at your antenatal appointments. Common reasons include your bump measuring large or small for your stage of pregnancy, a history of complications in previous pregnancies, certain medical conditions such as diabetes or high blood pressure, pregnancy with twins or more, or reduced fetal movements.
Some parents also choose to book a private growth scan in the third trimester for extra peace of mind, typically between 28 and 36 weeks.
What the Scan Measures
The sonographer will take four key measurements. Head Circumference and Biparietal Diameter measure the size of the head. Abdominal Circumference reflects the size of the baby's tummy and is sensitive to nourishment. Femur Length measures the thigh bone and indicates skeletal growth. Together these produce the Estimated Fetal Weight, usually given in grams or kilograms.
The scan may also assess amniotic fluid volume, placental position, and umbilical cord blood flow. All of these help build a complete picture of your baby's wellbeing.
Understanding Your Results
Your measurements are plotted on a customised growth chart, which takes into account your height, weight, ethnicity, and other factors. The important thing is the overall trend, not a single number.
The Estimated Fetal Weight has a margin of error of around 10 to 15 percent, so small differences between scans are normal. Your care team will look at the pattern of growth over time rather than relying on one measurement.
What If My Baby Is Measuring Small?
If your baby is measuring small, your care team may arrange a follow-up scan to check the growth pattern. They may also recommend Doppler measurements to check blood flow in the umbilical artery, and possibly additional monitoring.
What If My Baby Is Measuring Large?
A larger-than-average baby may simply reflect your build or genetics. In some cases it can be linked to gestational diabetes, so your care team may offer a glucose test.
Tips for Your Appointment
Wear loose clothing and bring your pregnancy notes. Ask the sonographer to explain what they are measuring and what the results mean.
Summary
A growth scan is a valuable, safe way to check that your baby is developing well in the later stages of pregnancy. Understanding what it measures and how to interpret the results can help you feel more informed and confident at your next appointment.