Uterine contractility during the menstrual cycle

The non-pregnant uterus shows different patterns of contractility during the menstrual cycle. A renewed interest in uterine contractility has resulted from reports of non-invasive ultrasound (US) based studies. To clarify the changes in uterine contractility occurring throughout the menstrual cycle, we prospectively studied uterine contractions (UC) at six representative stages with US and intrauterine pressure (IUP) based approaches in 30 cycling volunteers. Results showed UC frequency could be measured by either US or IUP. UC amplitude and resting pressure tone could only be assessed by IUP. Conversely, direction of UC displacement could only be assessed by US. UC frequency increased at mid-cycle and decreased throughout the luteal phase suggesting oestradiol and progesterone exert positive and negative actions on uterine contractility, respectively. UC amplitude increased throughout the menstrual cycle to maximum values in the late luteal phase. Retrograde UC were most frequent at mid-cycle and convergent ('opposing') UC predominated during the luteal phase. While the former pattern ensures sperm transport, the latter may facilitate embryo implantation. In conclusion, UC changes throughout the menstrual cycle assessed by US and IUP emphasize the hormonal dependence of uterine contractility. Although UC patterns favouring sperm transport appear regulated by oestradiol, uterine quiescence and the dominance of convergent UC prevailing at the time of implantation are linked to progesterone. These data will serve to identify and treat possible dyskinetic changes in uterine contractility, particularly in women suffering from infertility, endometriosis, and dysmenorrhea.