Myometrium was obtained from non‐pregnant 3‐month‐old [NP(3), n = 32 strips from n = 8, open bars with diagonal lines], late pregnant 3‐month‐old [LP(3), n = 32 strips from n = 8, open bars], non‐pregnant 5‐month‐old [NP(5), n = 32 strips from n = 8, closed grey bar with diagonal lines], late pregnant 5‐month‐old [LP(5), n = 32 strips from n = 8, closed grey bar], non‐pregnant 8‐month‐old [NP(8), n = 32 strips from n = 8, closed dark grey bar with diagonal lines] and late pregnant 8‐month‐old [LP(8), n = 32 strips from n = 8, closed dark grey bar] mice for (A), (B), (E) and (F). A, MIT was significantly higher in late pregnant myometrium compared to non‐pregnant myometrium across all age groups (***
P < 0.001, **
P < 0.01, *
P < 0.05). B, force amplitude was significantly higher in late pregnant myometrium compared to non‐pregnant myometrium across all age groups (**
P < 0.01, *
P < 0.05). C, representative trace showing spontaneous myometrial contractions from a late pregnant 3‐month‐old mouse. D, representative trace showing spontaneous myometrial contractions from a late pregnant 8‐month‐old mouse. E, spontaneous myometrial contraction frequency was significantly greater in late pregnant 8‐month‐old vs. late pregnant 3‐month‐old mice (*
P < 0.05). F, the myometrial spontaneous contraction duration was shorter in late pregnant 8‐month‐old vs. late pregnant 5‐month‐old and 3‐month‐old mice (**
P < 0.01). Data were analysed using ANOVA followed by an all pairwise multiple comparison Tukey's test and are presented as the mean ± SEM for (A), (B), (E) and (F); all significant comparisons (P < 0.05) comparisons are indicated.