The Unripe Cervix

Abstract

The central theme of the thesis is the phenomenon of cervical ripening which usually takes place during the last few weeks of pregnancy. Cervical ripening is recognised clinically by the changes which occur in the cervix, and these include softening of the tissues, progressive effacement and finally dilatation of the cervix. As these changes take place, the cervix becomes more anteriorly situated in the pelvis and the presenting part may descend. Based on these clinical criteria, a scoring system was developed which enabled an objective assessment of three central questions: 1. What mechanisms control cervical ripening? 2. What are the clinical implications of failure of cervical ripening? and 3. How may the clinical outcome for such patients be improved? The significance of an unripe cervix lies in its association with prolongation of pregnancy beyond term and vri.th increased maternal and fetal morbidity especially if labour is induced induced/by conventional methods. These problems are commoner and acre serious among primigravidae and so the research was concentrated on such patients. A major objective of the work described in this thesis was to examine how prostaglandins influenced cervical ripening and how they could be used therapeutically to improve the clinical outcome. The thesis begins with a historical review which is presented in two parts: a critical review of induction of labour, and an account of the discoverer, development and experience with prostaglandins up to the time the research was commenced. The historical review is followed by a discussion of the current understanding of the physiological control of cervical ripening. The clinical studies are then presented. By means of two studies, one retrospective and one prospective, amniotomy amniotomy/and intravenous oxytocin infusion is shown to be a satisfactory method of labour induction for primiparae who have ripe cervices before the onset of labour; in sharp contrast the two studies show that a poor response to this method of induction may be expected if the cervix is unripe at the time of amniotomy. Laboratory studies carried on in parallel with the clinical studies investigated the role of endogenous prostaglandins in parturition and cervical ripening. Prostaglandins of the E and F series were shown to increase sharply in the amniotic fluid between mid-pregnancy and term. Higher levels were found in early spontaneous labour than in than in/oxytocin induced labour at a time of greater uterine activity, and in both types of case the levels rose steeply during the active or acceleratory phase of labour. The levels of both E and F prostaglandins in amniotic fluid obtained at the time of amniotomy and oxytocin induction were found to be closely related to the degree of cervical ripeness, the uterine sensitivity to oxytocin and the length of Induced labour. The conclusions of the thesis are as follows:-1) The phenomenon of cervical ripening in late pregnancy is an essential part of the normal transition from pregnancy to spontaneous labour. 2) Failure of such ripening is an indication of an abnormality in the endocrine millieu of the pregnancy associated with impaired endogenous prostaglandin production. 3) Induction of labour by conventional means without regard to the condition of the cervix is likely to result in greater morbidity for those in whom it remains unripe. 4) The use of extra-amniotic prostaglandin therapy in such patients, either for induction of labour or for pre-induction cervical ripening, will go some way towards restoring their prospects of a satisfactory labour and delivery. Future research should be directed to further understanding of the mechanisms responsible for the spontaneous onset of labour. In this way, it is hoped that new techniques will be developed which will enable more precise control of uterine activity and cervical changes so as to ensure greater safety for both mother and child.