Crown Rump Length and Nuchal Translucency Calculator

Enter Measurements

Crown Rump Length (CRL), mm

Range supported by the original calculator: 2–85 mm.

Measured Nuchal Translucency (NT), mm (optional)

Leave blank to calculate gestational age (and expected NT) from CRL only.

Ultrasound / Scan date

Used to compute EDD from the CRL-based gestational age.

Results

EDD (based on CRL):

EDD = scan date + (280 days − CRL-based gestational age in days)

Measuring the CRL

"Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age" with accuracy of ±5–7 days. To measure the crown rump length (CRL) the image of the fetus or embryo is obtained in a true midsagittal plane . The maximum length from cranium (top of the head) to caudal rump (bottom) is measured as a straight line. When possible , the mean of three discrete CRL measurements should be used for estimating the due date.
REFERENCE Methods for estimating the due date. Committee Opinion No. 700.American College of Obstetricians and Gynecologists. Obstet Gynecol 2017;129:e150–4.