**5. Labor**

226 From Preconception to Postpartum

e.g. metabolites. Extended knowledge about these metabolites seems to be of importance, especially in the light of the clinical expression of labor dystocia (Steingrimsdottir et al. 1995). During the late 1980's and the 1990's several studies have been published on myometrial activity (Wedenberg et al. 1990; Wedenberg et al. 1991; Ronquist et al. 1993; Steingrimsdottir et al. 1995; Wedenberg et al. 1995). They have shown that the pregnant myometrium has a low energy charge (EC), described as an index of energy status, and compared with striated and cardiac muscles. The difference was considered to be due to the very special demand of the uterine muscle, compared to other muscles. The cardiac muscle has to work continuously, with only short periods of rest (diastole). Striated muscles must work instantly on command. The uterine muscle remains relaxed for long periods of time and then, only for short periods (labor), has to be transferred to a state in which strong contractions are required. This situation demand energy (Steingrimsdottir et al. 1993; Steingrimsdottir et al. 1995; Steingrimsdottir et al. 1997; Steingrimsdottir et al. 1999). Studies have shown an increased content of glucose in the pregnant smooth muscle in term pregnancy, compared with early pregnancy and the non- pregnant uterus. This finding along with a positive artriovenous difference in blood-glucose across the uterus (i.e. net uptake), indicates glucose to be the principal nutritive metabolite for the pregnant uterine

The anaerobic pathway seems to be more active in the myometrium than in striated muscles. The Lactate/Pyruvate ratio, an indicator of anaerobic metabolism, is reported to be higher in the pregnant myometrium compared with other muscles (Steingrimsdottir et al. 1995). The lactate content of pregnant uterine muscle has been reported to be doubled compare with the skeletal muscle, probably reflecting a vigorous glycolytic flow when the

The uterus undergoes a general metabolic preparation for a hypoxic condition in late gestation. A significant physiological alkalinisation of the muscle over the last few weeks of pregnancy has been shown (Parratt et al. 1995). This might therefore contribute to the mechanisms ensuring that strong and efficient contractions occur during labor, when acidity

A number of papers have been published on myometrial acid-base balance, and correlation to inefficient contractions and dysfunctional labor. One finding is that acidification of the myometrium with accumulation of lactate, and a decrease of myometrial pH during contractions, could depress uterine contractions and thereby contribute to dysfunctional labor. It has been shown that lactate concentration of myometrial capillary blood is significantly higher in women having a caesarean delivery due to dystocia than in women having an elective caesarean section or being operatively delivered with normal contractions. Furthermore, reduced pH and raised lactate concentrations in myometrial strips change regular contractions to irregular ones with reduced amplitude in vitro studies. One of the suggested clinical explanations for this process was that during labor blood vessel supply might be occluded while the uterus is contracting. The irregular contractile pattern in dysfunctional labor might lead to extended occlusion of the uterine vessels. Extended occlusion might lead to a lowering of the myometrial oxygen levels and accumulation of lactic acid. Thus, despite the inefficient contractions, there is an inadequate reoxygenation of the uterus. There is a suggestion that that there is a variation in response to intermittent hypoxia in different women. The recovery period

muscle (Steingrimsdottir et al. 1999).

is added during normal myometrial contractions.

from the low oxygen episode after occlusion might differ.

uterus is active.

"*In Africa the sun should never rise twice during labor, then it's dangerous*", an Old African saying was recounted by an African obstetrician at `Federation International Gynecologie Obstetrique´ (FIGO) 2006.
