Ultrasound Reference Chart Based on IVF Dates to Estimate Gestational Age at 6–9 weeks’ Gestation

Table 3

Estimated gestational age of 1268 fetuses derived from six existing CRL reference charts compared to IVF dates.

	𝑛	Range of differences to true gestational age in days	Mean difference (95% CI) in days	Comparison with true gestational age
ASUM	1233^*	−10.5 to 8	2.1 (2.0 to 2.2)	𝑃<0.0001
Hadlock	1268	−9 to 8	1.2 (1.1 to 1.3)	𝑃<0.0001
Daya	1268	−8 to 9	−0.57 (−0.67 to −0.48)	𝑃<0.0001
Verburg	271^*	−8 to 10	−1.2 (−1.5 to −0.81)	𝑃<0.0001
Old ASUM	1263^*	−9 to 8	0.43 (0.33 to 0.53)	𝑃<0.0001
Robinson	636^*	−7 to 10	0.39 (0.21 to 0.57)	𝑃<0.0001

A negative number denotes the number of days that estimated gestational age lagged behind true gestational age. ^*n values are less than 1268 because exact dates were not given for a number of CRL lengths in these charts. Verburg et al. [9], for instance, only provide exact dates for CRL lengths at 5, 10, and 15 mm.