The behavior of the uterine cervix during labor

Little appears to be kno'\vn about the relationship between behavior of the uterine cervix and myometrial activity during the first stage of labor.ns Considering the extensive medical and social problems related to dysfunctional behavior of the cervix during parturition, the lack of knowledge of cervical physiology and pathophysiology during labor is surprising. Labor dystocia, i.e. the failure of the cervix to dilate despite adequate uterine contractions, is the single factor that has contributed most to the increase in cesarean deliveries. On the other hand. preterm delivery is the most significant contributor to perinatal morbidity and mortality in the Western world. A better understanding of the physiology of cervical dilatation in relation to uterine contractions might contribute to the solution of these obstetric dilemmas. In order to improve the knowledge of the physiologic changes of the cervix during parturition. a reliable technique for monitoring cervical behavior during labor is indispensable. Until recently digital examination of the cervical os by the attending obstetrician \vas the only method available to assess the condition of the cervix during parturition. Using digital palpation of the cervix. Friedman demonstrated that the curve of cervical dilatation plotted against time is sigmoid-shaped. Although useful in everyday clinical practice. digital examination has major shortcomings. The inter-observer variability is considerable and the intermittent nature of the procedure does not allow an assessment of the dynamics of the cervix during labor. Despite these disadvantages, the knowledge of cervical changes during labor depends almost exclusively on data obtained by digital examination. For research purposes ultrasound cen·imetry seems to be the method of choice for measurement of cervical dilatation during labor. The ultrasound cervimeter uses two miniaturized transducers that are attached to the cervix to measure cervical dilatation during the first stage of labor. The method offers continuous recording of cervical dilatation during labor and can easily be combined with measurement of intrauterine pressure. thus allo\ving the assessment of cervical dynamics during labor. Interesting and promising results have been published in a preliminary report. For the first time. cervical dilatation patterns ·were objectively established. However insufficient clinical data are available to assess the potentials of ultrasound cervimetry and a thorough evaluation of its value is imperative. A second handicap for the study of cervical behavior during labor is the lack of insight into the mechanisms of control of cervical dilatation.18 Several observations suggest that prostaglandins are involved in the achievement of successful effacement and dilatation of the cervix. once cervical ripening is established. Prostaglandins have been shown to be important regulators of the physiology of the cervix during pregnancy, in particular during the last trimester. Concentrations of prostaglandin E2 en F2a rise markedly at the onset of labor and the accumulation of prostaglandins is less in labor progressing slowly than in labor of normal duration. However. thorough studies of prostaglandin-mediated cervical changes during. labor are lacking.