Prolonged or stalled labour can be a factor in poor neonatal outcomes. Labour progress is measured in terms of the rate of cervical dilatation over time and the descent of the fetus in the birth canal over time. The 'safe' duration of labour is a matter of controversy and, in some cases, the focus of a lawsuit. The failure to intervene where expected changes in cervical dilatation or fetal descent do not occur may give rise to liability for the obstetrical care provider.
Stages of Labour.
Labour can be divided into three stages. The first stage is from the onset of uterine contractions to full cervical dilatation at 10 cm. This first stage of labour can be further divided into two phases - latent phase and active phase.
The second stage of labour is from full cervical dilatation until delivery. The third stage involves delivery of the placenta. This article is primarily concerned with the active phase of the first stage of labour and the second stage of labour.
During the active phase of the first stage of labour uterine contractions promote cervical dilatation, needed to permit passage of the presenting part of the fetus, usually the head or 'vertex', down the birth canal. Uterine contractions can be characterized as the 'forces of labour', providing the needed pressure to efface (thin) and dilate the cervix.
These forces of labour not only promote progress, but also create a degree of 'stress' for the fetus. A well-grown, healthy, term fetus has a remarkable capacity to withstand the stress of uterine contractions (called 'fetal reserve') without adverse results, but this capacity has its limits. Where labour is too long and fetal stress too great, the capacity of the fetus to withstand these assaults can be exhausted, potentially leading to brain injury, or even death.
In the second stage of labour there is more active descent of the fetus. It ends with delivery. With pushing in second stage the stress on the fetus tends to be greater than that experienced during the active phase of the first stage of labour. After full cervical dilatation, there may be a period without pushing, called 'passive' second stage. With pushing it is called 'active' second stage. Active second stage is more stressful for the fetus.
A prolonged labour may be attributed to inadequate uterine contractions (power), a pelvis too small to allow progress (passage), or a fetus that is too large (passenger). In some cases that give rise to lawsuits, we find that obstetrical care providers may not have made the required efforts to tease out the reasons for a prolonged labour, leading to inadequate clinical response.
Labour Progression.
To evaluate labour progress during the active phase of the first stage of labour one must know when the active phase begins. The onset of active labour is a matter of some controversy in the medical literature. This controversy, I contend, is explained, at least in part, by a desire to defend obstetrical litigation.
Historically, many obstetrical units across North America adopted 4 cm of cervical dilatation as the onset of active labour. Others have argued that active labour begins at between 3 to 5 cm of cervical dilatation in the setting of regular uterine activity. Yet others argue for cervical dilatation of 6 cm to represent the onset of active labour.
As labour should more rapidly progress once active labour is achieved, criticism of obstetrical care is less likely with a later onset of labour (in terms of cervical dilatation). There is obstetrical literature that asserts that allowing a longer duration for cervical dilatation between 4 and 6 cm may reduce the cesarean section rate. These sorts of claims demand close scrutiny for what may be flawed analysis.
In the first-time mother the rate of cervical dilatation in the active phase of labour should be no less than 1.2 cm per hour. A rate of dilatation slower than 1.2 cm per hour should be considered a protracted labour or poor progress. For women who have already delivered once before, the rate of cervical dilatation should be at least 1.5 cm per hour.
Where there is no cervical change in active labour over a more prolonged period it may represent an 'arrest' of labour. Again, the time interval over which there is no change that will constitute an arrest of labour is also controversial. The longer one is prepared to tolerate no progress the less room there will be for criticism. Some have argued 2 hours while others 3 hours of no progress. Again, the longer the tolerable period of absent progress, the less likely that legal responsibility will attach.
Second stage labour in first time mothers has a median duration of about 50 minutes, with some as long as 3 hours. Yet, some obstetrical literature suggests a second stage as long as 5 or even 6 hours may be permissible. Once again, this calls for close scrutiny questioning the wisdom of these recommendations in the context in which they are made.
Fetal Stress.
Promoting longer active phase and second stage labour in the hopes of reducing cesarean section rates is, in my view, a potentially dangerous practice that could put the fetus at risk. As some have tried to contend recently, it may not be prudent to tie labour progress exclusively to time when the overall clinical picture is likely to have a bearing on safe obstetrical care.
That is, both maternal and fetal factors must be front and centre when assessing the adequacy of labour progress. The assessment of fetal reserve must figure prominently into a determination of safe labour in the clinical circumstances.
Uterine contraction patterns, a factor too often ignored in the cases we see in litigation, must also be important variables. Uterine contractions with abnormal features must be recognized for the potential to contribute to added fetal stress. Where fetal heart rate patterns deviate from normal, the obstetrical care provider must consider whether the fetus has the capacity to withstand a longer labour.
Prioritize Fetal Well-Being.
It is important not to lose sight of fetal well-being in the pursuit of lower cesarean section rates. Further, it is improper to counsel obstetrical care providers to accept slowly progressing labours as tolerable without careful evaluation of the clinical picture.
It is a mistake, in my view, to adopt 3 cm or up to 6 cm as the arbitrary onset of the active phase of the first stage of labour. With regular contractions, 3 cm is far preferable than 6 cm as representing the onset of the active phase. With irregular or mild contractions, later onset might be warranted. Further, induced or augmented labours may require other considerations, as do cases with epidurals on board.
I suggest that adverse neonatal outcomes from protracted or arrested labours are always avoidable. Resilience of the healthy term fetus may allow good outcomes even in the setting of poorly managed protracted labour, but this must not lead to complacency. It's like speeding down the highway at 200 km/hr - you may get to your destination unscathed, but why take the chance?
