Every antenatal appointment involves some form of measurement, and for many parents those measurements arrive with very little explanation. A sonographer writes a number on a screen. A midwife measures your bump with a tape measure. Someone asks about kick counts. What is actually being assessed, what the numbers mean, and what happens when something falls outside the expected range are questions that most parents have — and rarely feel they have the space to ask. This guide walks through each growth tracking method clearly, so that appointments feel less like a series of unexplained procedures and more like the informative encounters they are meant to be.

The Dating Scan: Your Baseline Measurement

The first formal measurement of your baby happens at the dating scan, offered between weeks 11 and 14. The sonographer measures the baby’s crown-rump length (CRL) — the distance from the top of the head to the base of the spine — to calculate gestational age and confirm or adjust your estimated due date.

This measurement is more accurate than calculating from your last period for many people, particularly those with irregular cycles or those who are uncertain of their dates. Once your due date is confirmed at the dating scan, it typically remains the reference point for all subsequent measurements throughout the pregnancy.

The Anatomy Scan: Growth and Structure Together

The anatomy scan at weeks 18–21 is the most comprehensive assessment of your baby’s development so far. Alongside the structural checks — brain, heart, spine, kidneys — the sonographer takes a series of biometric measurements:

• Head circumference (HC): The measurement around the baby’s head, which indicates brain growth
• Abdominal circumference (AC): The measurement around the baby’s abdomen, which reflects nutritional status and organ development
• Femur length (FL): The length of the thigh bone, used as a marker of overall skeletal growth
• Estimated fetal weight (EFW): Calculated from the above measurements — an estimate, not an exact figure

These measurements are plotted on growth charts that show where your baby sits relative to the expected range for their gestational age. A measurement that falls outside the standard range does not automatically indicate a problem — growth charts represent statistical averages across diverse populations, and individual babies vary considerably. Your sonographer or midwife will explain what any finding means and whether any follow-up is needed.

Fundal Height: The Tape Measure Measurement

From around week 24 onwards, your midwife will measure fundal height at each appointment — the distance in centimetres from the top of your pubic bone to the top of the uterus (the fundus). As a rough guide, fundal height in centimetres corresponds approximately to the number of weeks pregnant you are, though this relationship is not precise and is influenced by factors including your height, build, the baby’s position, and the amount of amniotic fluid.

Fundal height is a screening tool, not a diagnostic one. Its purpose is to identify pregnancies that may benefit from further investigation — either because growth appears to be slower than expected (small for gestational age) or faster (large for gestational age). If your fundal height is consistently outside the expected range, your midwife will typically refer you for a growth scan to get a more detailed assessment.

Growth Scans: When More Detail Is Needed

Growth scans — additional ultrasound appointments beyond the routine dating and anatomy scans — are offered when there is a clinical reason to look more closely at fetal growth. This might follow a fundal height measurement that falls outside the expected range, a pregnancy with certain risk factors, or a finding at the anatomy scan that warrants monitoring.

Being referred for a growth scan is not a signal that something is wrong. It is a signal that your care team wants better information than a tape measure can provide. Most growth scans are reassuring. When they identify a concern, having that information early allows for appropriate planning and monitoring.

Monitoring Baby’s Movements

From around 20 weeks, your baby’s movements become a meaningful indicator of wellbeing. You do not need to count a specific number of kicks — what matters is getting to know your baby’s individual pattern and noticing if it changes. A reduction in movement from what is normal for your baby should always be reported to your midwife or maternity unit promptly — the same day, not the next morning.

The Kicks Count campaign and Count the Kicks app offer practical, evidence-based guidance on monitoring movements. Do not be embarrassed to call your maternity unit if movements feel different — they will always want to hear from you.

“”Growth tracking in pregnancy is not about finding problems — it is about building a picture of your individual pregnancy over time. Single measurements matter far less than trends. A baby who is consistently growing along their own curve is almost always doing well, regardless of which centile that curve sits on.””

— Professor Jason Gardosi, director of the Perinatal Institute and founder of the GROW (Gestation Related Optimal Weight) customised growth chart programme. Professor Gardosi’s research has significantly shaped how fetal growth is assessed and interpreted in the UK, and his emphasis on individual growth trajectories rather than single-point thresholds is the principle that most directly informs how growth measurements should be understood by parents.

For a complete overview of what happens at each stage of pregnancy — including which appointments and scans occur when — visit our full Pregnancy Week by Week guide in the Pregnancy section.

Frequently Asked Questions

What does it mean if my baby is measuring small at a scan?

A baby measuring smaller than average at a single scan does not automatically mean there is a problem. Measurements carry a margin of error, and individual babies vary considerably in size. What matters most is whether growth is progressing consistently along the baby’s own trajectory. If your care team refers you for additional monitoring, this is a precautionary step to gather better information — not confirmation that something is wrong.

How accurate is estimated fetal weight from an ultrasound?

Estimated fetal weight from ultrasound biometric measurements has a margin of error of approximately 10–20%. This means a baby estimated at 3kg could weigh anywhere from around 2.4kg to 3.6kg. Ultrasound estimates are useful for identifying significant deviations from expected growth but should not be treated as precise predictions of birth weight.

My midwife said my fundal height is measuring large — should I be worried?

Not necessarily. Fundal height is a screening tool with significant variability — it is influenced by your build, the baby’s position, your bladder fullness at the time of measurement, and other factors. If your fundal height consistently measures outside the expected range, a growth scan gives a much clearer picture. Most growth scans following a large fundal height measurement are reassuring.

How often should I feel my baby move in the third trimester?

There is no specific number of movements that is “”correct”” — what matters is your baby’s individual pattern. From around 20–24 weeks, you will begin to recognise your baby’s usual activity level and timing. A reduction from that pattern — particularly if movements seem less frequent or less strong than usual — should be reported to your midwife or maternity unit the same day. Do not wait to see if things improve.

Will I definitely have a growth scan if my bump measures small?

It depends on your care team’s assessment and local protocols. A single measurement that is slightly below the expected range may result in a repeat fundal height measurement at the next appointment. Consistently small measurements, or measurements that fall below a specific threshold, typically result in a referral for a growth scan. Your midwife will explain the reasoning behind any referral clearly.

Key Takeaways

• Baby growth is tracked through a combination of ultrasound scans, fundal height measurements, and movement monitoring across the pregnancy.
• The dating scan (weeks 11–14) establishes your due date using crown-rump length; the anatomy scan (weeks 18–21) takes detailed biometric measurements.
• Fundal height in centimetres broadly corresponds to weeks of pregnancy and is used as a screening tool from week 24 onwards.
• A single measurement outside the expected range is less significant than a consistent trend; individual babies vary considerably in size.
• Movement monitoring from around 20 weeks is a key indicator of baby wellbeing — a change in your baby’s usual pattern should always be reported promptly.
• Growth scans are precautionary, not diagnostic — most produce reassuring results.

Understanding what is being tracked, and why, transforms antenatal appointments from a series of unexplained measurements into a meaningful ongoing conversation about your pregnancy. Each measurement is a data point in a picture that builds over time — and you are a full participant in that picture, not just the subject of it. Ask the questions. Ask for the explanations. You are entitled to understand every aspect of your care.