Enter ultrasound measurements
Use values from your scan report. Units are applied to all measurements.
Example data table
| Scenario | BPD (mm) | HC (mm) | AC (mm) | FL (mm) | Output (typical) |
|---|---|---|---|---|---|
| Mid‑pregnancy scan | 52 | 190 | 165 | 36 | GA ≈ 22w • EFW ≈ 500–600 g |
| Later scan | 82 | 300 | 290 | 62 | GA ≈ 33w • EFW ≈ 2000 g |
| Partial data (AC+FL) | — | — | 220 | 48 | GA from AC+FL • EFW from Hadlock 1 |
Formula used
Unit handling: Inputs can be in mm or cm; calculations use cm.
Estimated fetal weight (EFW): Hadlock models compute log10(EFW), then EFW(g) = 10^{log10(EFW)}.
- Hadlock 1: log10(W) = 1.304 + 0.05281·AC + 0.1938·FL − 0.004·(AC·FL)
- Hadlock 2: log10(W) = 1.335 − 0.0034·(AC·FL) + 0.0316·BPD + 0.0457·AC + 0.1623·FL
- Hadlock 3: log10(W) = 1.326 − 0.00326·(AC·FL) + 0.0107·HC + 0.0438·AC + 0.158·FL
- Hadlock 4: log10(W) = 1.3596 − 0.00386·(AC·FL) + 0.0064·HC + 0.00061·(BPD·AC) + 0.0424·AC + 0.174·FL
Gestational age (GA): Hadlock 1984 regression equations estimate menstrual age in weeks from single or combined parameters. The calculator can show a chosen equation or a practical “best” option that prefers more complete inputs.
| Inputs | Equation (weeks) |
|---|---|
| BPD | MA = 9.54 + 1.482·BPD + 0.1676·BPD² |
| HC | MA = 8.96 + 0.540·HC + 0.0003·HC³ |
| AC | MA = 8.14 + 0.753·AC + 0.0036·AC² |
| FL | MA = 10.35 + 2.460·FL + 0.170·FL² |
| BPD+AC+FL | MA = 10.61 + 0.175·(BPD·FL) + 0.297·AC + 0.710·FL |
| BPD+HC+AC+FL | MA = 10.85 + 0.060·(HC·FL) + 0.670·BPD + 0.168·AC |
How to use this calculator
- Select the unit that matches your report (mm or cm).
- Enter any available biometry values: BPD, HC, AC, and FL.
- Choose a GA method and an EFW model, or keep defaults.
- Optionally add scan date and last menstrual period to compare dating.
- Click Calculate to view GA, EDD, and estimated weight above the form.
- Use Download CSV for a spreadsheet, or Download PDF to print to file.
FAQs
1) What is ultrasound biometry?
It is a set of fetal measurements taken on ultrasound, such as head, abdomen, and femur dimensions. These values help estimate growth patterns, gestational age, and approximate fetal weight during pregnancy.
2) Which measurements does this tool use?
It can use BPD, head circumference, abdominal circumference, and femur length. You can enter any subset. The calculator selects equations that match the measurements you provide.
3) Why do different weight formulas give different results?
Each model was derived from different datasets and combinations of measurements. Small differences in coefficients can change the estimate, especially later in pregnancy. That is why the mean of available models can be helpful.
4) How accurate are these estimates?
Ultrasound weight estimation has an intrinsic error margin, and accuracy varies with gestational age, fetal position, and measurement technique. Use results as supportive information, not a final diagnosis.
5) What does “Best GA” mean here?
This calculator prefers equations that use more measurements when available, because combined-parameter dating is often more stable than relying on a single number. You can also select a specific equation.
6) Can I use this to confirm a due date?
It can estimate an ultrasound-based due date from the scan date and calculated gestational age. Due date decisions should follow your clinician’s guidance and your pregnancy’s overall context.
7) Why compare ultrasound dating with LMP dating?
LMP dating reflects cycle history, while ultrasound dating reflects current biometry. Comparing them can highlight discrepancies that may need a review of dates, measurement quality, or clinical follow-up.
8) Does this replace medical advice?
No. This tool is for education and planning discussions. Always confirm measurements, interpret results with your care team, and seek urgent care for concerning symptoms.