Rima Patel1, Lucilla Poston1 and Rachel M Tribe1. 1Women’s Health Academic Centre, King’s College London. London SE1 7EH, UK. Background: Advanced maternal age (defined as ≥35 years at delivery) is associated with adverse obstetric risks including operative delivery, stillbirth, and post-term labour induction. The physiological causes for such complications remain to be ascertained, although myometrial function has been implicated (Smith GC et al., 2011; Arrowsmith et al., 2012). To address the hypothesis that maternal age directly influences successful parturition, we assessed timing of birth and fetal outcome in a pregnant mouse model. The function of myometrium and cervix ex-vivo was also examined. Methods: Gestation length (days) and parturition duration (hours) in young (3 months old, n=8) and old (8 months old, n=8) nulliparous pregnant C57/BL6 mice were monitored using infrared cameras. The number of viable pups delivered per mouse was recorded. Isolated myometrial tissues from pregnant (day 18) C57/BL6 mice (3 months and 8 months; n=10 each group) were used for isometric tension recording [spontaneous contractility; mean integral tension (g) and contractile frequency (Hz)]. Oxytocin induced contractility (n=5 for both groups) was also measured [mean integral tension(g)]. Maximal cervical distensibilty (mm) was recorded in cervices from pregnant (day 18) C57/BL6 mice (3 months and 8 months, n=5 per group). Results: Older pregnant mice compared to 3 month old mice had a longer mean (±SEM) gestation (20.08 ±0.49 days vs. 19.05 ±0.25; p<0.001) and significantly longer labours (3.68 ±0.83 hours vs. 1.01 ±0.41; p<0.001). The 3 month old mice gave birth to a greater number of viable pups compared to older mice (7.5 ±0.53 vs. 4.8 ±2.2, p<0.01); 50% of older mice had at least one stillborn pup. The contractile frequency of myometrium ex-vivo was faster in older pregnant mice (0.05 ±0.0098 vs. 0.02 ±0.0046 Hz, p<0.05); however mean integral tension was similar. The 8 month group appeared to exhibit a greater sensitivity to oxytocin (n=5, 10-10 – 10-9 M), but this did not reach significance. Cervical distensibility was significantly greater in older pregnant mice (19.4 ±0.60 vs. 16.6 ±0.75 mm, p<0.05). Conclusions: Gestation length, labour duration and stillbirth risk were increased in older pregnant mice suggesting that there is an intrinsic problem with parturition processes in older mice. This is unlikely to be due to delayed cervical ripening as evidenced by enhanced distensibility in older mice. However, the increased contraction frequency seen in older mice ex-vivo could potentially result in poorly coordinated myometrial contractions in-vivo.