Background: Voltage-gated potassium (Kv) channels are involved in the regulation of spontaneous myometrial contractions in vitro and are hypothesised to contribute to uterine quiescence in early pregnancy. The precise molecular identity of the channels has yet to be determined, but we have previously reported that Kv7 channels, encoded by KCNQ1-5 and/or β-accessory subunits encoded by KCNE genes (1-5), are present in non-pregnant mouse myometrium. In this study, we have examined the expression of KCNQ and KCNE genes in myometrium from early and late pregnant mice and compared expression to non-pregnant tissues. We have also investigated the functional impact of Kv7 channels in pregnancy using pharmacological agents. Methods: Myometrial tissues were obtained from non-pregnant (at the time of oestrous), early pregnant (day 6-7) and late pregnant (day 17-18) C57/BL6 mice. Total RNA was extracted using Trizol and cDNA synthesised with Superscript III. qRT-PCR for KCNQ1-5 and KCNE1-5 was quantified using a standard curve and data expressed relative to the geometric mean of the two most stable housekeeping genes from a panel of 5. Myometrial strips were used for isometric tension recording and activity measured as mean integral tension (MIT) ±XE991/chromanol (Kv7 inhibitors) or retigabine/flupirtine (Kv7 activators). Results: All of the KCNQ and KCNE isoforms studied were detected in mouse myometrium. There was a general suppression of all KCNQ isoforms, with the exception of KCNQ3, in early pregnancy (n= 6, p < 0.001) compared to myometrium from non-pregnant (n=6) and late pregnant (n= 6) animals. This is in contrast to the high expression levels of KCNQ1 and KCNQ5 in myometrium from non-pregnant and late pregnant mice. KCNE isoforms were also gestationally regulated. KCNE1, KCNE3 and KCNE5 expression was decreased in late-pregnant compared to non-pregnant tissues (p<0.05)and KCNE2 and KCNE4 expression was increased in tissues from early and late pregnant mice compared to tissues from non-pregnant animals (p < 0.001). XE991 (10 µM) significantly increased spontaneous myometrial contractions in all tissues studied (p < 0.05) and retigabine/flupirtine (20 µM) attenuated myometrial contractility (p<0.01). Interestingly chromanol 293B (1-30 µM) had no impact on contractility. Conclusions: The expression profile of KCNQ and KCNE isoforms in the myometrium is distinct to other smooth muscles. KCNQ isoforms are generally suppressed in early pregnancy but expression levels are restored to non-pregnant levels in late gestation. Kv7 channels modulators impact on non-pregnant and pregnant myometrial contractility suggesting a significant role for these channels in myometrial function. Supported by Tommy’s the Baby Charity (registered charity no: 1060508)