Gestational Age / EDD from Ultrasound

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Biology, Medicine & Pharmacology (educational estimates only — every panel labeled not-medical-advice)

Tranche

tranche-4

Evidence ID

t4-264

Ledger rows

1

No ledger note is attached.

Review findings

The arithmetic formulas are standard conditional formulas for propagating an already-established ultrasound gestational age and calculating a 280-day EDD. The exact unresolved ambiguity is whether the interface supplies a current/today date and whether GA_at_scan is entered in days, weeks-and-days, or another unit. The existing estimate-only and not-medical-advice labeling is appropriate, but the interface should also state that ultrasound dating inputs must come from an appropriate clinical method and should define valid GA ranges and date handling.

Formula and scope findings

• GA_today=GA_at_scan+days_elapsed is standard only when GA_at_scan and days_elapsed are both expressed in elapsed calendar days; the specification does not define the required today/current-date input.
• EDD=scan_date+(280−GA_at_scan_days) is the standard 280-day gestational-age calculation conditional on a valid ultrasound-based GA at scan, but the specification does not provide a formula for deriving GA from CRL or other biometry.
• The claimed CRL/biometry capability is underspecified: the listed inputs contain only scan date and GA at scan, not CRL, biometric measurements, measurement units, or a reference dating chart/model.

Unit assumptions

• GA_at_scan must be an integer or precisely defined fractional number of gestational days; if entered as weeks and days, it must be converted first, for example 12 weeks 3 days = 87 days.
• days_elapsed must mean calendar days from the scan date to the requested current date, not elapsed 24-hour periods across time zones or daylight-saving transitions.
• EDD is a calendar date calculated using 280 total gestational days, equivalent to 40 weeks.
• Date arithmetic must use a defined calendar, including leap-year handling and a date-only timezone-independent representation.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The specification exposes two failure hazards: invalid calendar dates can produce undefined results unless rejected, and interpreting GA_at_scan as weeks instead of the formula's indicated days changes the EDD from 2025-02-16 to 2024-10-19. The formula also requires a leap-year calendar branch at February 29.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "scan_date": "2025-01-15",
    "ga_at_scan_days": 84,
    "today": "2025-02-12"
  },
  "expected_outputs": {
    "current_ga_days": 112,
    "current_ga": "16 weeks 0 days",
    "revised_edd": "2025-07-30"
  },
  "working": "days_elapsed = 2025-02-12 − 2025-01-15 = 28 days. current GA = 84 + 28 = 112 days = 16 weeks 0 days. Remaining gestation = 280 − 84 = 196 days. EDD = 2025-01-15 + 196 days = 2025-07-30."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json