Fetal Head Circumference | Growth Tracker

How to use this trackerTap to view instructions

Track several ultrasounds for the same fetus on one graph, or use the page for a single calculation.

Start a new case. Select + New case, enter a nonidentifying case code, and choose Create. An estimated due date (EDD) is optional. For a one-time result, leave "One-time calculation - not saved" selected and press Calculate HC after entering HC and GA.
Enter an ultrasound. Enter the examination date, gestational age, and HC in millimeters. If an EDD was saved, the page fills in gestational age from the scan date. For a one-time result, select Calculate HC; the result and clinical report appear below. No case is needed.
Save the measurement. With a case selected, click Save measurement. The point is added to that case's graph and to the Saved measurements table below.
Add the next ultrasound to the SAME case. On a later visit, reopen this page in the same browser, select the existing case from the list (do not create a new one), enter the new date and HC, and click Save measurement again. All saved measurements appear together on the graph.

Clear or reset: Use Reset entry in Step 2 to clear only the unsaved form. Use Erase all saved cases in Step 1 to delete all saved cases and measurements (after confirmation).

Where are records saved? Only in this browser on this device and website; not in the EMR or on another device. They may be lost if browser/site data are cleared. Download a backup regularly. Never enter names, MRNs, or other patient identifiers.

Offline use on iPhone: When this page and its companion offline files are hosted on HTTPS, open it online once, then use Share then Add to Home Screen. After the offline cache is ready, the installed web app can be reopened without internet. Saving remains on that device; export backups regularly. A single downloaded HTML file can calculate offline but its saved-case persistence may vary in iPhone file previews.

1Choose one-time or saved case

Calculation mode / saved case

For one measurement, leave One-time calculation selected. Enter HC and GA, then tap Calculate HC. No case required.

Case settings (due date / delete)

Estimated due date

EDD can automatically fill gestational age from the ultrasound date. Updating it does not change past saved ages.

Clear all saved data - permanently removes every locally saved case and its ultrasound measurements.

2Enter ultrasound measurement

Ultrasound date (optional)

GA weeks

Days

HC (mm)

Add an optional ultrasound note

Note (no patient identifiers)

Create or choose a case to save.

Reset entry clears unsaved inputs (or cancels editing). It does not delete saved measurements. In one-time mode no data are saved.

For serial tracking, keep the same case selected and enter a new ultrasound date and HC. Each saved scan becomes another point on the chart.

3Result and growth chart

Head circumference - Enter HC and GA

Approximate SD position - SMFM / Chervenak reference

Reference HC at this gestational agemillimeters (mm)

Enter HC and GA to show reference values.

Enter gestational age and HC to see the result.

HC growth plot

Chart view

Mean-1 SD-2 SD-3 SD-5 SDYour measurements

Reading the plot: Blue filled circles show saved scans; the outlined circle marks the current entry. The lightly shaded areas separate the -2 to -3 SD and -3 to -5 SD reference bands; they are not diagnostic categories. Tap a saved point to edit. On iPhone, swipe horizontally to see the whole plot.

Graph reference: SMFM Publications Committee, AJOG 2016;214:B2-B4, Table B3; adapted from Chervenak et al., AJOG 1984;149:512-517, Table III. SD curves use the historical reference and are linearly interpolated between completed weeks.

Clinical report for EMR

The report separates measurement, prior trend, interpretation, and follow-up considerations. Review/edit as needed after pasting; nothing is automatically entered into the EMR.

Saved measurements

Choose a case to keep measurements between visits.

These are the scans saved for the selected case. Use Edit to correct a saved entry. A new visit is added above in Step 2.

Ultrasound date	GA	HC (mm)	Approx. SD	Interpretation	Action
No saved measurements yet.

Other options & references

How the HC measurement is calculated

Reference values are transcribed from the table in the 2016 SMFM Statement, adapted from Chervenak et al. (1984). At whole weeks the displayed curves match the published table. Values at days 1-6 are linearly interpolated between neighboring whole-week entries. A displayed SD position is approximated by interpolation between adjacent published SD bands (mean, -1, -2, -3, -4, -5 and, above the mean, +1/+2 from Chervenak Table III). It is not an independently validated continuous Z-score model. Results beyond +/-2 or -5 SD are capped rather than extrapolated.

Do not assume that a percentile or another HC formula can be substituted for this specific standard. Small changes in chart, date, and measurement technique may change the classification. The reference covers 20+0 to 42+0 weeks only.

Clinical interpretation and limitations

The 2016 SMFM publication specifically concerns ultrasound screening after Zika exposure, not a current universal diagnostic protocol. It recommends evaluation of intracranial anatomy when HC is more than 2 SD below the mean and follow-up ultrasound in 3-4 weeks if anatomy is normal; isolated fetal microcephaly is defined at or below -3 SD. The historical publication described measurements at or below -5 SD as particularly concerning.

ISUOG's 2024 third-trimester ultrasound guideline also describes microcephaly as commonly defined below -3 SD and emphasizes assessment of head shape, brain anatomy and cortex. Prenatal HC alone cannot establish a neurologic prognosis. The graph shows observed values, not a growth-velocity reference or diagnostic trend line. A concerning measurement warrants confirmation of gestational dating, appropriate technique, neurosonographic assessment and individual clinical evaluation.

Local data: backups, imports and limitations

Click Download all cases (JSON) below to keep a backup. To restore later, click Import backup (replaces current saved cases). To remove all locally saved data, use Erase all saved cases in Step 1 (Choose a case). Data are stored in this browser's local storage on the same device and site origin. They are not encrypted, not sent to a server, not automatically backed up, not synchronized, and may disappear if site data are cleared, private browsing is used or browser privacy policies intervene. File-based local storage behavior can vary, especially in iPhone file previews. For reliable repeat use, host the full offline package via HTTPS and add the page to the iPhone Home Screen after visiting online. The offline cache works only after it is installed; browser storage can still be cleared by the user or device. Do not use actual patient identifiers or rely on it as the official medical record. For identifiable patient tracking in practice, integrate an authenticated, audited, encrypted EHR-backed store instead.

Exported files are unencrypted; store or transfer them only using an approved secure workflow. Import replaces all saved cases after confirmation.

Full citations

Society for Maternal-Fetal Medicine (SMFM) Publications Committee. Ultrasound screening for fetal microcephaly following Zika virus exposure. Am J Obstet Gynecol. 2016;214(6):B2-B4. doi:10.1016/j.ajog.2016.02.043. [Mean and SD table, page B3.]
Chervenak FA, Jeanty P, Cantraine F, et al. The diagnosis of fetal microcephaly. Am J Obstet Gynecol. 1984;149(5):512-517. doi:10.1016/0002-9378(84)90027-9. [HC/head perimeter, Table III.]
Khalil A, Sotiriadis A, D'Antonio F, et al. ISUOG Practice Guidelines: performance of third-trimester obstetric ultrasound scan. Ultrasound Obstet Gynecol. 2024;63(1):131-147. doi:10.1002/uog.27538.

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