Defining the abnormal first stage of labour
Defining an abnormal latent phase of labour is problematic. It is known that the latent phase encompasses the progressive effacement and dilatation of the cervix. The latent phase ends with a fully effaced cervix, the dilatation at which this occurs being less important and also a matter of some controversy.
The latent phase may occur without symptoms. It may be heralded by a show but even this symptom is not universal. Women presenting in spontaneous labour are more commonly already in the active phase of labour. This makes any attempt to define the normal duration of the latent phase purely speculative. Women who are in the delivery suite and diagnosed as being in the latent phase are likely to either have been misdiagnosed to be in labour or requiring induction of labour.Friedman defined the latent phase of labour as being prolonged if it lasted more than 20 hours in the nulliparous woman or 14 hours in the multiparous woman (16). These limits may reflect what was viewed as an acceptable length of time to subject a woman to the stresses of labour. The dictum ‘never let the sun set twice on a labouring woman', implying that women can be allowed to labour for up to 48 hours reflects the prevalent thinking in obstetrics up to the mid twentieth century. Management of labour in that era was largely expectant. With improvements in asepsis and anaesthesia, the caesarean section evolved from a potentially lethal procedure reserved for dire situations to save a mother's life to a safe operation that is used for maternal and fetal benefit. Prolonged labours can also be emotionally traumatic for women and increase demands on staff and resources. Adverse maternal and fetal sequelae may also result. It is for these reasons that in present-day obstetrics, labours are not usually allowed to continue for as long as initially suggested by Friedman.
O'Driscoll and colleagues at the National Maternity Hospital in Dublin, Ireland proposed the concept of the AML which comprises a package of measures including a limit of12 hours on the duration of active labour (17). It is noteworthy that the other tenets of AML are:• a policy of non-interference for women in the latent phase or who are not in labour
• regular assessment of cervical dilatation
• early intervention by amniotomy and/or oxytocin infusion if labour progresses slowly
• one-to-one care by a midwife.
The 12-hour limit in AML would therefore refer to the active phase of labour with women in the latent phase being managed expectantly. While there are no defined limits of what the observed length of the latent phase should be, such as in women undergoing induction of labour with oxytocin, obstetricians may intervene by caesarean section in women who remain in the latent phase for 12 hours.
The minimum acceptable rate of progress for the active phase of the first stage of labour was defined by Friedman as 1 cm/hour in nulliparous women and 1.5 cm/hour in multiparous women. This standard has more recently been challenged with the suggestion that normal labour progresses somewhat slower. The 2014 National Institute for Health and Care Excellence (NICE) guidelines for intrapartum care (18) in the United Kingdom state that the minimum acceptable rate of progress in the active phase of the first stage of labour is 0.5 cm/hour.
An abnormal first stage of labour can essentially be classified into the following three categories:
1. A prolonged latent phase—because the duration of the latent phase cannot be defined, this is best defined as a latent phase that lasts longer than is acceptable to the labouring woman and her caregivers.
2. Primary dysfunctional labour—progress which is slower than the accepted rate of progress but which continues until full dilatation is achieved. This pattern is common in nulliparous women.
3. Secondary arrest—a halt in progress in the active phase of labour prior to full cervical dilatation.