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 daysMean difference (95% CI) in daysComparison with true gestational age

ASUM1233*−10.5 to 82.1 (2.0 to 2.2) 𝑃 < 0 . 0 0 0 1
Hadlock1268−9 to 81.2 (1.1 to 1.3) 𝑃 < 0 . 0 0 0 1
Daya1268−8 to 9−0.57 (−0.67 to −0.48) 𝑃 < 0 . 0 0 0 1
Verburg271*−8 to 10−1.2 (−1.5 to −0.81) 𝑃 < 0 . 0 0 0 1
Old ASUM1263*−9 to 80.43 (0.33 to 0.53) 𝑃 < 0 . 0 0 0 1
Robinson636*−7 to 100.39 (0.21 to 0.57) 𝑃 < 0 . 0 0 0 1

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.