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Fetal Gestational Age Chart
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Quickly check fetal gestational age using ultrasound measurements like Crown-Rump Length (CRL) and Head Circumference (HC). Covers all trimesters to help you track fetal development.
This is a locally maintained static reference table, not a live official directory, current policy or complete collection. Records without a named source and update date remain unverified.
CRL dating equation from INTERGROWTH-21st (2014), restricted to CRL 22–79 mm and rounded to days: 40.9041+3.21585×sqrt(CRL)+0.348956×CRL. The study enrolled pregnancies at 9+0–13+6 weeks. Unsourced HC/BPD/FL lookups were removed. A research-equation reference, not diagnosis or individual pregnancy dating. Reference
Overview
Understand what the tool solves, how it works, and the boundaries of its data.
This reference matches a crown–rump length (CRL) measurement in millimeters to an equation-based gestational age in days and weeks-plus-days. It uses the INTERGROWTH-21st 2014 CRL dating equation and displays whole-millimeter entries from 22 through 79 mm. In this notation, 10+2 means 10 completed weeks and 2 additional days. CRL is the measured length from the crown of the head to the rump on an ultrasound image.
The equation is gestational age (days) = 40.9041 + 3.21585 × √CRL + 0.348956 × CRL, with CRL entered in millimeters; the resulting days are rounded to the nearest whole day. For example, 35 mm gives about 72 days, displayed as 10+2. The table is a compact lookup of that calculation, rather than a full fetal growth chart or a personalized pregnancy dating service. The underlying study enrolled pregnancies dated from 9+0 to 13+6 weeks. The original study record and INTERGROWTH-21st pregnancy dating resources describe the research context.
Guide
Follow the workflow and verify inputs and outputs with practical examples.
Use the CRL value recorded by the ultrasound provider. Check that it is expressed in millimeters; do not enter a value in centimeters as though it were millimeters.
Find the same whole-millimeter CRL in the reference table. Each row pairs the measurement with an equation estimate in weeks and days, as well as the rounded day count.
For a row showing 10+2, read this as 10 weeks and 2 days. The separate day value is the same estimate expressed as a total number of days, not a second result.
As a check, the 35 mm row corresponds to 72 days, or 10 weeks and 2 days. A value between listed whole-millimeter rows is not separately calculated by the table.
Use cases
See how the tool fits into real work and everyday tasks.
A reader can use a reported CRL to find the corresponding equation estimate and understand the weeks-plus-days format before discussing the report with the clinician who performed or reviewed the scan.
A student or educator can compare the same value in days and weeks-plus-days, then inspect the cited study to understand the research population behind the reference.
Q&A
Find concise answers to common questions and confusing cases.
It means 10 completed weeks plus 2 days. The day total is another way to display the same rounded estimate.
No. The equation and table use millimeters. Convert the report value to millimeters before looking it up; for example, 3.5 cm is 35 mm.
No. It provides CRL rows only. It does not contain second- or third-trimester measurements or combined biometric estimates.
The reference only lists whole-millimeter CRL values from 22 through 79 mm. It does not provide an out-of-range estimate or interpolate between entries; ask the clinician interpreting the scan which reference applies.
Notes
Review scope, result limitations, and important precautions before use.
This is an arithmetic reference based on one published CRL equation, not a medical assessment. Its 22–79 mm table range corresponds to estimates from 9+0 to 13+6; the study population and method do not establish an individual patient’s gestational age.
Do not use a table result to set or revise an individual due date, diagnose a condition, or resolve a difference between an ultrasound report and other dating information. Pregnancy dating should be interpreted by a qualified clinician using the complete clinical context. This page does not supply a diagnostic reference for head circumference, biparietal diameter, abdominal circumference, femur length, or later-pregnancy measurements.
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