Fundal Height and Gestational Age Relationship
All international guidelines universally recommend measuring fundal height with a tape measure in the third trimester as a screening tool for fetal growth abnormalities, with the measurement in centimeters correlating to gestational age in weeks between 18-32 weeks. 1
Standard Measurement Technique and Correlation
Fundal height should be measured from the pubic symphysis to the top of the uterine fundus using a tape measure, with the measurement in centimeters approximately equaling gestational age in weeks. 1, 2
The correlation between fundal height and gestational age is most reliable between 18-32 weeks of gestation, with a growth rate of approximately 1 cm per week during this period. 3
After 32 weeks, the rate of fundal height growth slightly decreases, making the correlation less predictable in late third trimester. 3
Key Anatomical Landmarks by Gestational Age
- At 12 weeks: Fundus palpable at the pubic symphysis
- At 16 weeks: Fundus midway between symphysis and umbilicus
- At 20 weeks: Fundus at the umbilicus (20 cm)
- At 20-32 weeks: Fundal height in cm = weeks of gestation (±2-3 cm is normal variation)
- At 36 weeks: Fundus reaches the xiphoid process
- At 40 weeks: Fundus may drop slightly as fetal head engages
Recommended Charting Methods
Three of six international guidelines (50%) specifically recommend plotting fundal height measurements on customized growth charts, while two guidelines (33%) recommend using the McDonald rule (fundal height >3 cm less than gestational age in weeks indicates concern). 1
The McDonald rule defines suboptimal growth when fundal height is >3 cm less than gestational age in weeks. 1
Customized growth charts account for maternal characteristics and have been associated with improved detection of small-for-gestational-age babies and reduction in stillbirth through programs like the UK's Growth Assessment Protocol. 1
Clinical Limitations and When to Use Ultrasound
Four guidelines (67%) specifically recommend ultrasound scans instead of fundal height in women with obesity and/or fibroids, as fundal height measurements are unreliable in these populations. 1
The sensitivity of fundal height for detecting fetal growth restriction is only 17.3%, though specificity is 92-95%, making it a poor screening tool but useful for ruling out abnormalities when normal. 4
Fundal height sensitivity is even lower (reduced further) in overweight/obese women but higher in multiparous women. 4
Manual fundal height and ultrasound measurements of fundal height are equivalent (R² = 0.92), confirming that the technique itself is reliable when properly performed. 2
Clinical Action Thresholds
When fundal height measurement lags >2-3 cm behind expected gestational age, ultrasound evaluation for fetal growth restriction should be performed. 1
All guidelines recommend umbilical artery Doppler studies when small-for-gestational-age is suspected based on fundal height discrepancy, as this guides surveillance frequency and delivery timing. 1
Serial fundal height measurements showing inadequate growth velocity (crossing percentiles downward) warrant ultrasound evaluation even if absolute measurements remain within normal range. 1
Common Pitfalls to Avoid
Failing to use a consistent measurement technique (always measure from pubic symphysis to fundal top with tape measure, bladder empty, patient supine)
Relying on fundal height alone in obese patients where sensitivity drops significantly—proceed directly to ultrasound in these cases 1
Not plotting serial measurements on a chart—single measurements are less useful than tracking growth trajectory over time 1
Ignoring fundal height-dates discrepancy in multiparous women, where sensitivity for detecting growth abnormalities is actually higher 4
Using outdated population charts from the 1980s that may not reflect current maternal weights and body habitus 1