Growth scans in pregnancy: why you might have one

A growth scan is an extra scan later in pregnancy to see how your baby is growing. Being offered one doesn’t mean something is wrong. Here’s why they’re done and what the results can mean.

How growth is checked

In lower-risk pregnancies, your midwife measures your bump at antenatal appointments (the symphysis fundal height, or SFH). The NHS says this starts from around 25 weeks. One hospital trust says its midwives measure from 28 weeks and plot the measurement on a growth chart. If the measurement is lower or higher than expected, you’re referred for a scan.

Who is offered growth scans?

Some people are offered scans routinely because of risk factors. One trust gives examples such as smoking, past raised blood pressure or a previous small baby. Others are offered when measuring the bump isn’t reliable, for example if you have a higher BMI or fibroids, or if the bump measurement was lower than expected. NHS Scotland guidance (for the lower-risk pathway) says to arrange a scan within 3 days if the first measurement is below the 10th centile, and within 5 days if it is above the 97th. Exact rules differ between hospitals and nations.

What happens at a growth scan?

The sonographer measures your baby’s head, tummy and thigh bone to estimate weight, which is compared with a chart for your stage of pregnancy. They may also check blood flow in the umbilical cord and elsewhere with a Doppler, and the amount of fluid around your baby.

What does ‘small for dates’ mean?

One NHS trust explains that small for gestational age means the estimate is in the lowest 10% for that stage of pregnancy. It says most of these babies are healthy, keep gaining weight and have normal blood flow. Fetal growth restriction is different: it means a baby isn’t growing as well as expected, often because the placenta isn’t working as well as it should, and it needs closer monitoring. Your team will tell you which applies and what the plan is.

If your baby is measuring small, you may be invited back for a scan every 2 to 3 weeks to check growth, fluid and blood flow. In most cases the trust says there is nothing you did or could have done differently.

How accurate are they?

Estimates aren’t exact. The same trust says scan estimates can vary by up to 20% at the end of pregnancy, so a measurement is one piece of the picture.

If your baby’s movements slow down, stop or change, call your midwife or maternity unit straight away, day or night. Don’t wait until the next day, and don’t use a home doppler or a phone app to check the heartbeat, because they aren’t reliable.

Questions people ask

What if a scan says my baby is big?

A measurement is one part of the picture. Your team will explain what it means in your case and talk through your options.

Did I cause it?

In most cases, one NHS trust says, there is nothing you did or could have done differently. If you’d like support with anything, such as stopping smoking, your midwife can help.

Do growth scans use a different type of scan?

No. They use the same ultrasound as other scans.

What if I’m worried about my baby’s size?

Tell your midwife. They can check or arrange a scan if needed.