Measurement of VZ during the early stages of pregnancy. The box plots show VZ between Days 1.5 and 5.5 post-coitus (n = 12 each). The horizontal line within the box shows the median, and the dotted line within the box shows the mean value. ● Represents outliers. The data were evaluated using the Shapiro–Wilk normality test and Student’s t-test (*P < 0.005, ***P < 0.05) or Wilcoxon’s rank-sum test (**P < 0.001).