Calculator: Nuchal translucency (NT) percentile for measured crown-rump length (CRL)

Input

Crown-rump length
Nuchal translucency

Results

Important: Inputs must be complete to perform calculation.


Gestational age by crown-rump length
Expected nuchal translucency
Nuchal translucency percentile

Decimal precision

Notes

For more information on the use of nuchal translucency, refer to UpToDate topic reviews on enlarged (increased) nuchal translucency.

Equations used

Gestational age by crown-rump length = e^{(1.684969+(0.315646*Crown-rump length/10)-(0.049306*(Crown-rump length/10)²)+(0.004057*(Crown-rump length/10)³)-(0.000120456*(Crown-rump length/10)⁴))}

Expected nuchal translucency = 0.437 + (0.01969 * Crown-rump length)

Nuchal translucency percentile = 50 + ((Nuchal translucency - Expected nuchal translucency) / 0.02044444)

Calculation details and variables

The Nuchal translucency percentile equation was derived from analysis of table 1 and figure 2 of the Chung article.^[2] Percentiles are calculated by linear interpolation of the published 5^th, 50^th, and 95^th expected NT percentiles.
Example NT-CRL percentiles^[2] and calculated 99^th percentiles are listed in the table below.

References

Appendix

Example NT-CRL percentiles

	Expected NT (mm)
CRL (mm)	50^th percentile^[2]	95^th percentile^[2]	Calculated 99^th percentile
45	1.32	2.24	2.33
55	1.52	2.44	2.53
65	1.72	2.64	2.72
75	1.91	2.83	2.92
85	2.11	3.03	3.12

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Topic 144871 Version 1.0

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Calculator: Nuchal translucency (NT) percentile for measured crown-rump length (CRL)