Trunk circumference offers an alternative to crown-rump length for determination of gestational age in the first trimester. Unfortunately its measurement overlaps with the thoracic or abdominal circumference and often defaults to the latter.
gestational age in weeks =
= 6.23 + (0.16 * (trunk circumference in mm)) - (0.0011 * ((trunk circumference in mm) ^2))
where:
• trunk circumference is in the range of 10 to 70 mm
• gestational age is in the range of 7 to 12 weeks
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