Quick answer: At every antenatal appointment from around week 20, your midwife or OB will measure your fundal height — a tape measure from your pubic bone to the top of your uterus.
At every antenatal appointment from around week 20, your midwife or OB will measure your fundal height — a tape measure from your pubic bone to the top of your uterus. Despite its low-tech appearance, this measurement provides genuinely useful information about fetal growth.
How Fundal Height Is Measured
With you lying flat on your back, your provider locates the top of the uterus (fundus) by palpation, then runs a flexible tape measure from the pubic symphysis over the abdomen to the fundus. The result in centimeters is recorded. The key principle: fundal height in centimeters approximately equals gestational age in weeks, ± 2cm (McDonald’s rule). At 26 weeks, expected fundal height is approximately 24–28cm. After week 36, as the baby’s head descends into the pelvis, the fundal height may plateau or slightly decrease.
Normal Range and What It Tells Us
Measurements within 2cm of gestational age are reassuring. Measurements persistently more than 2cm from expected indicate ultrasound is needed for more accurate assessment. They’re not in themselves diagnostic of a problem. Important factors affecting fundal height independently of fetal size: maternal BMI (higher BMI reduces accuracy), fibroids, baby’s position, amniotic fluid volume, placenta position, and natural variation in uterine position.
Small for Dates: What It Can Mean
Fundal height measuring more than 2cm below gestational age can indicate: fetal growth restriction (FGR) — baby not growing adequately, potentially from placental insufficiency; oligohydramnios (reduced amniotic fluid); baby in a position making the height measure low; or measurement variation between providers (common). Ultrasound follow-up is standard — providing estimated fetal weight, growth percentile, amniotic fluid index, and umbilical artery Doppler assessment.
Large for Dates: What It Can Mean
Measuring more than 2cm above gestational age can indicate: large for gestational age (LGA) baby — often associated with gestational diabetes; polyhydramnios (excessive amniotic fluid); multiple pregnancy (if not already known); or uterine fibroids. Again, ultrasound provides the definitive picture. Fundal height is a screening tool, not a diagnosis.
Scans That Follow Up Abnormal Fundal Height
Ultrasound assessment when fundal height triggers concern typically includes: Growth biometry scan — measures head circumference, abdominal circumference, and femur length; calculates estimated fetal weight and plots on a growth chart. Amniotic fluid assessment — AFI (amniotic fluid index) or maximum vertical pocket measurement. Umbilical artery Doppler — assesses blood flow resistance through the umbilical artery; elevated resistance can indicate placental insufficiency. Biophysical profile — scores fetal movement, breathing movements, tone, and fluid volume.
Frequently Asked Questions
Why does fundal height vary between providers?
It’s a manual measurement with inherent inter-observer variability — different hands place the tape at slightly different anatomical points. Studies show up to 3cm variation between experienced providers. This is why trends over time (consistent measurement by the same provider) are more meaningful than comparing single readings across different providers.
My fundal height is 2 weeks behind — should I worry?
Not necessarily — but it warrants a growth scan. Measurements 2cm behind gestational age are at the lower limit of normal and commonly caused by baby’s position, lower amniotic fluid, or natural uterine positioning variation. An ultrasound provides precise fetal weight assessment. If the scan shows normal growth and fluid, no intervention is needed.
Is fundal height reliable if I’m overweight or obese?
Fundal height has lower accuracy with higher BMI — adipose tissue makes accurate palpation of the fundus and pubic symphysis more difficult. Some guidelines recommend serial growth scans rather than tape measurement for women with BMI over 35. Discuss the most appropriate monitoring approach for your individual situation.
Related Reading
- Your body at 1 week pregnant: what’s really happening
- 20 weeks pregnant: halfway there – anatomy scan guide
- 28 weeks pregnant: kick counts and why they matter
- Can I use a dummy or pacifier?
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