Control and assessment of the uterus and cervix during pregnancy and labour

Preterm labour and resultant preterm birth are the most important problems in perinatology. Countless efforts have failed to establish a single effect ive treatment of preterm labour, partly because the mechanisms regulating t he uterus and cervix during pregnancy are not well understood. New knowledg e is needed to inhibit early progression of labour (uterine contractility a nd cervical ripening), and adequate quantitative tools to evaluate the uter us and cervix during pregnancy are lacking. In this review we outline studi es showing that the uterus (myometrium) and cervix pass through a condition ing step in preparation for labour. This step is not easily identifiable wi th present methods to assess the uterus or cervix, In the uterus, this seem ingly irreversible step consists of changes in the electrical properties to make muscle more excitable and responsive to produce forceful contractions , In the cervix, the step consists of softening of the connective tissue co mponents, Progesterone appears to have a dominant role in controlling both the uterus and cervix, as antiprogestins induce early, preterm conditioning leading to preterm labour. Apparently, nitric oxide (NO) also controls con ditioning of the uterus and cervix, Ire the uterus, NO, in concert with pro gesterone, inhibits uterine contractility. At term, NO production by the ut erus and placenta are decreased and allow labour to progress, in contrast? NO in the cervix increases at the end of pregnancy and it may be the final pathway for stimulating cervical ripening by activation of metalloenzymes, The progress of labour can be assessed non-invasively using electromyograph ic (EMG) signals front the uterus (the driving force for contractility) rec orded from the abdominal surface. Uterine EMG bursts detected in this manne r characterize uterine contractile events during human and animal pregnancy . A low uterine EMG activity, measured transabdominally throughout most of pregnancy, rises dramatically during labour. EMG activity also increases su bstantially during preterm labour in humans and rats. This method may be us ed one day to predict impending preterm labour sand identify control steps and treatments. A quantitative method also assesses the cervix, using an op tical device which measures collagen fluorescence in the cervix. The collas cope estimates cervical collagen content from a fluorescent signal generate d when collagen cross-links are illuminated with excitation light of about 340 mn, The system has proved useful in rats and humans at various stages o f pregnancy, and indicates that cervical softening occurs progressively in the last one-third of pregnancy. In rats, collascope readings correlate wit h resistance measurements made in the isolated cervix, which may help to as sess cervical function during pregnancy, and indicate control and treatment s.