Enter a fundal height (SFH) in cm to see its percentile for a given gestational age, or switch modes to estimate GA from SFH. You’ll also get the expected SFH, standard deviation, and a ± GA band.
How the estimate works
- Reference pattern: in uncomplicated singleton pregnancies, median SFH in centimeters tracks roughly with GA in weeks from about 20 to 36 weeks. The model uses this common clinical rule-of-thumb as its core mean curve.
- Edges of the window: before ~20 weeks, SFH rises more slowly; after ~36 weeks, the curve flattens. The tool applies gentler slopes in these regions to reflect typical charts.
- Population spread: a constant SD near the mid-gestation band with slightly wider SD at earlier and later weeks captures usual measurement variation between people and examiners.
- Percentile math: for “SFH percentile at GA,” the entered SFH is compared with the mean and SD at that GA using a normal-distribution approximation to output an approximate percentile.
- GA from SFH: for “estimate GA from SFH,” the model inverts the mean curve to find a best-fit GA, then creates a ± band by converting the SD in centimeters to weeks using the local slope of the curve.
Assumptions and caveats
- Singleton focus: the estimates assume a singleton pregnancy. Multiple gestations, obesity, uterine fibroids, fetal lie, and examiner technique can shift SFH independently of fetal growth.
- Screening tool: SFH is a screening measure. Concerning values or trends typically lead to ultrasound for fetal size, amniotic fluid, and dopplers as indicated.
- Rounding: outputs are rounded for readability. Small day-to-day differences are common and often reflect technique or fetal position.
What the tool shows
- Percentile mode: GA at measurement, entered SFH, approximate percentile, and typical SFH with SD at that GA.
- SFH → GA mode: estimated GA (weeks + days) and a typical range in weeks that reflects usual measurement variability.
Limitations
- Uses simplified mean and SD profiles; clinic-specific charts may differ.
- Does not incorporate maternal characteristics, parity, or ethnicity-specific customized charts.
- Not validated for conditions that alter uterine size or palpation (e.g., fibroids, polyhydramnios, oligohydramnios).
- Clinical practice texts and guidelines describing SFH as a screening tool with expected cm ≈ weeks from 20–36 weeks and referral to ultrasound for discordant measurements.
- Observational studies and reviews reporting measurement variability of SFH across gestation and factors that affect accuracy (maternal BMI, fetal lie, examiner technique).
- Antenatal care manuals outlining how to measure SFH, interpret trends, and trigger further assessment when growth concerns arise.
How to use this calculator
- Select a mode: “Percentile at GA” or “SFH → GA”.
- Enter the fundal height (SFH) in centimeters.
- For percentile mode, add the gestational age (weeks+days). For SFH → GA mode, GA is estimated for you.
- Read the outputs: SFH percentile with the expected SFH and SD, or an estimated GA with a ± band.
Educational only. SFH can be affected by fetal position, bladder fill, fibroids, BMI, and twins. Ultrasound dating and growth scans guide care if there are concerns.
Last updated: September 21, 2025
Frequently asked questions
What does fundal height (SFH) measure?
SFH is the distance from the pubic symphysis to the top of the uterus. In mid-pregnancy, SFH in centimeters often approximates weeks of gestation.
How accurate is SFH for dating?
SFH is a screening tool. It’s less precise than ultrasound for dating. Use Ultrasound Due Date for the best GA estimate when available.
Why might my SFH percentile be high or low?
Normal reasons include fetal position, bladder fill, body habitus, and measurement variation. Persistent low or high percentiles may prompt an ultrasound. If your dates are uncertain, compare with the Pregnancy Due Date Calculator.
Does this work for twins?
SFH is less reliable with multiples. For planning in twins, use the Twin & Triplet Due Date Calculator and follow your clinician’s scan schedule.
What units does the tool use?
Centimeters. If your measurement is in inches, convert to cm before entering (1 inch = 2.54 cm).
When should I contact my clinician?
Seek care for decreased fetal movement, painful contractions, fluid leakage, or if SFH is consistently very different from expected. Ultrasound guides next steps when needed.