Statistical evaluation of ultrasound versus light microscopy measurements. Bland-Altman analyses of the relationship between measurements obtained by ultrasound (UBM) in vivo and by light microscopy (LMM) ex vivo for (A) crown-rump length (CRL), (B) biparietal diameter (BPD), (C) anterioposterior abdominal dimension (APD), and (D) placental diameter (PD). The difference between paired measurements are plotted against the mean of the two measurements. Each point shows the paired results obtained in one conceptus. The solid line in each graph shows the bias between the two measurement methods. The bias was not significantly different from zero for all four variables. The dashed lines show the ± 95% confidence intervals.