Fundal height by week checker

What does my fundal height measurement mean?

Somewhere after 24 weeks, an appointment starts to include a tape measure across your bump, and a number gets written in your notes. Often nothing is said about it. Sometimes something is said in passing — “measuring a bit small”, “measuring ahead” — and you leave holding a comment without a context. This page is for that situation.

What is actually being measured

Symphysis fundal height is the distance from the top of the pubic bone to the top of the uterus, in centimetres. It is a proxy for the size of the uterus and, indirectly, for how the baby is growing. It has been in use for a very long time because it costs nothing, harms nobody and can be done anywhere.

In the UK, NICE guideline NG201 sets out when it should happen: at each antenatal appointment after 24+0 weeks, no more often than every two weeks, for a single baby, unless you are having regular growth scans instead. If you are on a scan pathway — because of a previous small baby, certain medical conditions, or a twin pregnancy — the scan is what your care follows and the tape measure is not central.

The rule everyone repeats

From around 24 weeks, the measurement in centimetres roughly matches the number of weeks pregnant you are, within about 2 to 3 centimetres. At 32 weeks, something in the region of 29 to 35 centimetres would not raise an eyebrow.

It is a useful mental shortcut, and it is also weaker than its fame implies. As a screening test for a small baby, fundal height misses a large share of the babies it is looking for, and raises concern about many babies who are simply small and entirely well. It is retained because the alternative — scanning everyone repeatedly — has its own costs and its own false alarms.

Why your chart matters more than the rule

A single number compared against a single expected value ignores the fact that women are different sizes. A woman of 150 centimetres and a woman of 180 centimetres should not be held to the same expected fundal height, and a first baby and a fifth baby do not produce the same measurements.

This is why many UK maternity services plot fundal height on customised charts, adjusted for maternal height, weight, parity and ethnic group. What is being watched is the line, not the point: a measurement that sits consistently along its own trajectory is reassuring in a way that one reading can never be, and a measurement that flattens off is informative even if it is still inside the expected band.

Why the number moves when the baby has not changed

Fundal height is a physical measurement made by a person with a tape, on a moving target, through a layer of abdominal wall. A full bladder can add a centimetre or two. The baby's position changes it. Fibroids change it. Amniotic fluid volume changes it. And two clinicians measuring the same woman minutes apart routinely get different answers.

Because of this, most services try to have the measurement taken the same way each time and plotted by someone looking at the previous points. If your notes show a jump between two appointments, the most likely explanations are measurement variation or a change in position, not a sudden change in your baby.

If you are told you are measuring small or large

NICE is clear about what follows, and it is the same thing in both directions: a scan. If there is concern that you are measuring large for dates, an ultrasound for growth and wellbeing should be considered. If there is concern that you are measuring small, a scan should be offered, and how quickly depends on what else is going on — reduced fetal movements or raised blood pressure would make it more urgent.

What does not follow is a diagnosis. Measuring small does not mean your baby is growth restricted; most babies who measure small on a tape are found on scan to be growing normally. Measuring large does not mean you have gestational diabetes or that you will need a caesarean. The tape measure is a way of deciding who gets a closer look, and that is the whole of its job.

Please do not measure yourself

It is tempting, and it is not useful. The measurement depends on landmarks that are hard to find on yourself, on a consistent technique, and on being plotted against your own previous points on your own chart. A number you generate at home has none of that behind it, and the most likely outcome is either false reassurance or a night of unnecessary fear.

What is genuinely worth monitoring at home is your baby's movements. A change in the pattern of movements matters at any gestation and should prompt a call to your maternity unit the same day, whatever any measurement has said. Fundal height does not override that, and a reassuring measurement last week is not a reason to wait.

The short version

Fundal height is a cheap, imprecise screening tool, measured from 24 weeks, plotted on a chart, and read as a trend rather than a verdict. The centimetres-equals-weeks rule is a rough guide with a wide margin. If someone has expressed a concern about yours, the next step is a scan and it will usually be reassuring. If nobody has said anything about your number, that is because it did not need saying.