Cephalopelvic disproportion

Oxytocin is contraindicated in patients with known hypersensitivity to the drug, cephalopelvic disproportion, unfavorable fetal position or presentation, in obstetric emergencies, situations of fetal distress when delivery is not imminent, severe toxemia (preeclampsia, eclampsia), hypertonic uterus, during pregnancy (intranasal administration), when there is total placenta previa, or to induce labor when vaginal delivery is contraindicated. Oxytocin is not expected to be a risk to the fetus when administered as indicated. When oxytocin is administered with vasopressors, severe hypertension may occur. 

Contraindications to oxytocin include fetal distress, prematurity, abnormal fetal presentation, cephalopelvic disproportion, and other predispositions for uterine rupture. 

Women with a history of six or more deliveries and anomalies of the fetus (for example hydrocephalus causing cephalopelvic disproportion) must also be excluded. 

However, uneventful vaginal deliveries have been reported in patients with two previous cesarean sections in whom labor was induced with vaginal PGE2 (121). Women with a history of six or more deliveries and anomalies of the fetus (for example hydrocephalus causing cephalopelvic disproportion) must also be excluded. 

AUGMENTATION OF DYSFUNCTIONAL LABOR To augment hypotonic contractions in dysfunctional labor, it rarely is necessary to exceed an infusion rate of 10 mlU/min, and doses of >20 mlU/min rarely are effective when lower concentrations fail. Potential complications of overstimulation include trauma of the mother or fetus due to forced passage through an incompletely dilated cervix, uterine rupture, and compromised fetal oxygenation due to decreased uterine perfusion. Oxytocin usually is effective when there is a prolonged latent phase of cervical dilation and when, in the absence of cephalopelvic disproportion, there is an arrest of dilation or descent. 

Normal delivery is based on the complex interaction of maternal factors, fetal properties, and adequate labor. If this interaction of Passages, Passenger, and Powers is disturbed, labor is protracted or even arrested. The failure of labor to progress is therefore not a diagnosis but a symptom that is amenable to treatment (e.g. when caused by inadequate uterine contractions) or not (e.g. absolute cephalopelvic disproportion). Isolated evaluation of either of the three factors, passages, passenger, and powers, is of limited value as, for instance, cephalopelvic disproportion can be diagnosed only if one looks at both the maternal pelvis and the fetus ( this pelvis is too small for this fetus ). 

Failure of adequate progression of labor due to cephalopelvic disproportion with imminent fetal asphyxia is the most common reason to perform secondary cesarean section. Arrest is typically caused by a combination of a large infant, an abnormal birth mechanism, and a narrow maternal pelvis. Detectable abnormal narrowing with an absolute disproportion occurs in 0.5%-l% of all deliveries today (Fig. 14.1). The incidence of borderline pelvic findings in which the size of the child and the birth mechanism together decide whether spontaneous delivery will be possible is much higher (Table 14.1). 

Assistance in women with hypoactive and uncoordinated contractions is recommended if progression is delayed and cephalopelvic disproportion has been excluded as the cause. Oxytocin is the drug of first choice [5]. 

Only few published studies have investigated the role of external pelvimetry. A prospective cohort study of primiparous African women showed that a combination of maternal height measurement and clinical external pelvimetry can identify a subgroup of patients with a high likelihood of cephalopelvic disproportion [18]. Comparable studies that present recent and robust data for western countries are not available. 

Following publication of these results, the rate of primary cesarean sections for breech presentations increased to up to 80%. Nevertheless, spontaneous delivery in breech presentation may be the preferred option of the mother. In such cases it is particularly important to exclude cephalopelvic disproportion. 

Only 0.5%-l% of all pregnant women have such obvious pelvic anomalies that absolute cephalopelvic disproportion is highly likely. The risk of abso-... 

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