Management of the prolonged first stage of labour

The prolonged latent phase

Women may be diagnosed to be in the latent phase of labour be­cause they present with a show or prodromal or Braxton-Hicks con­tractions. Vaginal examination findings of a cervix that is not fully effaced would support this diagnosis.

If an amniotomy is performed inadvertently or intentionally in these women, delivery becomes mandated. The next intervention is an oxytocin infusion to optimize uterine contractions in the hope that labour will progress beyond the latent phase and into the active phase of the first stage. If labour does not progress within the time limits which are acceptable, intervention by caesarean section be­comes necessary. Reference was made earlier in this chapter to the 20-hour limit for nulliparous women and 14 hours for multiparous women proposed by Friedman and the fact that shorter durations would be the norm in modern obstetrics.

Primary dysfunctional labour

This pattern of labour exhibits a slow but continued progress in the active phase and is common in nulliparous women. The treatment for primary dysfunctional labour is to ensure efficient uterine con­tractions. This is achieved by performing an amniotomy, if the mem­branes are intact, or commencing an oxytocin infusion. The aim is to achieve five uterine contractions every 10 minutes but not more fre­quent than this. More than five contractions in 10 minutes is termed tachysystole and may induce fetal intolerance as manifested by ab­normal fetal heart rate patterns.

Once contractions are optimized, progress of labour is often re­stored. If this does not happen, there is still a place for expectant management as long as progressive cervical dilatation occurs.

Secondary arrest

Causes of an arrest in progress of cervical dilatation in the active phase can be classified as the three Ps. These factors must be present to ensure normal progress of labour:

1. Powers—adequate uterine contractions.

2. Passages—an adequately large pelvic cavity as a conduit for the fetus.

3. Passenger—a fetus which is not excessively large.

The only ‘P’ over which the obstetrician has any control is the powers. Confirming that efficient uterine activity is present is the first step in managing secondary arrest. An amniotomy (if mem­branes are intact) or an oxytocin infusion are the available inter­ventions to correct inadequate uterine contractions. There is a case to consider an oxytocin infusion even in women who demonstrate regular uterine contractions as the strength of the contractions is not possible to assess clinically. This is particularly so in nulliparous women who more frequently require augmentation with oxytocin. Augmentation is also safer in nulliparous women whose risk of uterine rupture from this intervention is so low that they are often termed to be immune to it (19).

Once uterine contractions have been optimized, secondary arrest of labour is due to either cephalopelvic disproportion (CPD) or fetal malposition.

Cephalopelvic disproportion

As the name suggests, this cause of secondary arrest is due to a mis­match in fetal size and diameters of the pelvis. Fetal macrosomia can be as a result of maternal diabetes or genetic predisposition (a ‘constitutionally large’ fetus). A contracted bony maternal pelvis is a rare cause of CPD today but was a common sequelae of rickets two centuries ago. Occasionally, women with an acquired cause of a contracted pelvis such as a history of traumatic fractures of the pelvis may be encountered. As neither an excessively large fetus or an abnormally small pelvis are common in clinical practice, CPD is more likely to be a subtle mismatch between fetus and pelvis with the diagnosis being inferred by demonstrating secondary arrest in the absence of fetal malposition.

Fetal malposition

The fetus in the occiput anterior presentation adopts a well-flexed attitude. This results in a vertex presentation where the presenting diameter, the suboccipitobregmatic diameter, is the smallest possible anteroposterior fetal cephalic diameter to negotiate the maternal pelvis. As a result, occipitoanterior positions are optimal for spon­taneous vaginal birth unless an unusually large baby or unusually small maternal pelvis is present. The same is not true in malpositions such as an occipitoposterior or occipitotransverse position. In these situations, although there is no cephalopelvic disproportion in the absolute sense, the wider and therefore less optimal fetal diameters must negotiate the maternal pelvis. This can result in secondary ar­rest of labour. Often, optimizing uterine contractions may correct the malposition and allow the labour to progress. If this spontaneous flexion and rotation to an occiput anterior position does not occur, with persistent malposition and failure to progress with increasing moulding and caput, recourse to caesarean section may need to be considered.