[Uterine contractile activity at embryo transfer--as a new pharmacotherapeutic target in assisted reproduction]

Uterine contractile activity plays an important role in the reproduction of mammals, influencing sperm transport in the genital tract and positioning of the implanting embryo within the uterine cavity In humans, apart from the time of menses, the activity of a non-pregnant uterus is usually not perceived, and it is also not a subject of any routine clinical testing. Major contractile factors in non-gravid uteri are oxytocin and prostaglandins, locally produced within the endometrium. Oxytocin synthesis and expression of its receptors is gradually increasing in the follicular phase, following an increase in estrogen levels, and reaches its peak in the periovulatory period. In stimulated cycles, where supraphysiological estradiol concentrations are present, uterine contractile activity can be elevated. Exaggerated uterine contractions before embryo transfer are observed in one third of women undergoing controlled ovarian stimulation. Detection of such patients could enable their qualification for pharmacologic treatment. Evaluation of uterine contractions in such cases should be done non-invasively in order to avoid any endometrial trauma. Ultrasound evaluation of the movements of endometrial interface can be applied. Pharmacologic treatment of elevated uterine contractility before embryo transfer could improve the success rates of fertility treatments. So far application of beta mimetics or non-steroid anti-inflammatory drugs has not been associated with any progress. Oxytocin receptor system in the myometrium and the endometrium is a potential target for new class of medications aiming to improve implantation rates. This review summarizes up-to-date knowledge on the significance of uterine contractile activity in embryo implantation and describes the emerging new treatment targets in assisted reproduction.