Fundal Height Percentile Calculator
Enter the gestational age and measured symphysis-fundal height to compare the measurement with the INTERGROWTH-21st international standard for singleton pregnancies.
Fundal height percentile57.32%
- Z-score
- 0.18
- Expected median fundal height
- 27.68
- Difference from median
- +0.3 cm
- 10th-90th percentile range
- 25.5 to 29.9 cm
- 3rd-97th percentile range
- 24.5 to 30.9 cm
- Percentile band
- 10th to 90th percentile
INTERGROWTH-21st centiles at this gestational age
| Centile | Fundal height |
|---|---|
| 3rd | 24.46 |
| 10th | 25.49 |
| 50th | 27.68 |
| 90th | 29.88 |
| 97th | 30.91 |
Uses the INTERGROWTH-21st singleton pregnancy symphysis-fundal height equations.
This calculation does not apply to twin or higher-order multiple pregnancies.
A single measurement cannot show whether growth is slowing or accelerating across visits.
How to use this calculator
- Enter the completed weeks of pregnancy from the established dating.
- Enter any additional days beyond the completed week.
- Enter the fundal height in centimeters from a non-elastic tape measurement.
- Read the percentile together with the z-score, median, and reference ranges.
How the fundal height percentile is calculated
This calculator applies the INTERGROWTH-21st symphysis-fundal height equations for healthy singleton pregnancies. It first converts the entered gestational age to exact weeks:
GA = completed weeks + additional days / 7
The expected median fundal height in centimeters is:
M = 5.133374 + 0.1058353119 * GA^2 - 0.0231295 * GA^2 * ln(GA)
The gestational-age-specific standard deviation is:
S = 0.9922667 + 0.0258087 * GA
With measured fundal height H, the z-score is:
Z = (H - M) / S
The percentile is the standard normal cumulative probability for that z-score, multiplied by 100. Very small or very large percentiles are shown as <0.1% or >99.9% so the display does not imply more precision than a single tape measurement can support.
How to read the ranges
The 50th percentile is the median from the equation. The 10th and 90th percentile values use M - 1.28 * S and M + 1.28 * S. The 3rd and 97th percentile values use M - 1.88 * S and M + 1.88 * S. These are population reference centiles, not diagnostic cutoffs by themselves.
The gestational age usually moves the expected value most because both the median and the standard deviation change with week and day. The measured fundal height then determines how far above or below that week's median the result falls. Dating uncertainty, tape placement, fetal position, maternal body composition, fibroids, and amniotic-fluid volume can all move a real-world measurement.
What the calculator leaves out
The calculation uses the singleton reference only. It does not adjust for twins or higher-order multiples, measurement technique, fetal presentation, maternal habitus, uterine fibroids, amniotic-fluid volume, fetal sex, or local clinical protocols. It also treats one measurement as one point in time; it cannot decide whether growth is slowing, accelerating, or crossing centiles between visits.
Clinical interpretation depends on accurate pregnancy dating and serial assessment. A result below the 10th percentile or above the 90th percentile may lead a clinician to repeat the measurement, review technique and dating, or consider ultrasound assessment, but the calculator itself does not diagnose fetal growth restriction, macrosomia, or any other condition.
Worked example
Suppose the pregnancy is dated at 28 weeks 0 days and the measured fundal height is 28.0 cm. The exact gestational age is 28 + 0 / 7 = 28.0 weeks. The INTERGROWTH-21st equation gives a median of 27.68 cm and a standard deviation of 1.71 cm.
The z-score is (28.0 - 27.68) / 1.71 = 0.18, which corresponds to about the 57.32nd percentile. The difference from the median is +0.3 cm, the 10th-90th percentile range is 25.5 to 29.9 cm, and the 3rd-97th percentile range is 24.5 to 30.9 cm.
Common questions
What should fundal height be at my week of pregnancy?
Fundal height often roughly tracks gestational weeks in the middle of pregnancy, but the exact expected value is not simply one centimeter per week. This calculator uses the INTERGROWTH-21st median and standard deviation for the exact week and day you enter.
Is fundal height supposed to equal gestational weeks?
It can be close, especially after about 20 weeks, but it does not have to match exactly. The reference median is curved across pregnancy, and normal measurements spread around that median. Technique and anatomy can also change the tape measurement.
What does a fundal height below the 10th percentile mean?
It means the entered measurement is below the 10th centile of the singleton reference for that gestational age. That can happen for reasons that are not fetal growth restriction, including dating uncertainty, fetal position, maternal body composition, or measurement variation. A clinician may compare serial measurements or use ultrasound when the clinical picture calls for it.
What does a fundal height above the 90th percentile mean?
It means the measurement is above the 90th centile of the reference for the entered gestational age. Possible contributors include measurement technique, uterine fibroids, fetal position, amniotic-fluid volume, and fetal size. The percentile alone does not diagnose macrosomia or excess fluid.
Can this calculator be used for twins?
No. The INTERGROWTH-21st fundal height standard used here was developed for singleton pregnancies. Twin and higher-order multiple pregnancies need clinical interpretation that is not represented by this calculation.
Why can my fundal height percentile change between appointments?
Percentiles can move because the uterus grows, the expected median changes with gestational age, and measurements have normal variability. A single point cannot show growth velocity. Serial measurements taken with consistent technique are more informative than one isolated percentile.