When giving birth in a hospital setting, most women are aware that as soon as they arrive in labour, they are put ‘on the clock’. They will be offered and will probably accept vaginal examinations on arrival and every 3-4 hours afterwards.

Related reading: Vaginal Examinations – 7 Things You Shou ld Know.

Their care providers might suggest certain interventions to keep labour on track and progressing at a certain pace, in accordance with hospital procedures and the traditionally expected rate of cervical dilation, based on the Friedman curve over the first and second stages of labour. What many women aren’t aware of is the reasoning behind this fixation on centimeters and time.

What is Friedmans curve? An explanation

In 1955, Dr Friedman, from Columbia University, published a pioneering study investigating the association between cervical dilation and labour duration. He studied a sample of 500 first-time white mothers, who all gave birth at full term.

Of the 500 births that he sampled:

There were 14 breech births (2.8%)
There were 4 twin births (0.9%)
4 were still births or neonatal deaths
96% of women were sedated.

The doctor plotted their labours on a graph and calculated the average time it took a woman to dilate each centimetre. This graph is known as the Friedmans Curve and it has been used as the ‘gold standard’ for rates of cervical dilation and fetal descent during the active phase of labour for more than 60 years.

Why is Friedmans curve, or ‘labour curve’, used?

The Friedman curve came about to understand how cervical dilation changes over time. Understanding how labour progresses and how the cervix dilates over time brought order and a ‘science’ to analysing labour progression. The use of a labour curve was then used to determine which labours were progressing at the desired rate and which were falling behind. The labour curve became a tool used to decide which labours were ‘prolonged’ and therefore required medical intervention, in an attempt to reduce associated complications.

What are the parts of the Friedmans curve?

From his research observations, Friedman detected 4 phases of progression within the first stage of labour:

Latent phase – with little change in cervical dilation
Acceleration phase – the brief period that links the latent to the maximal phase
Maximal dilation phase – the phase where labour progresses most quickly, from around 3-4 cm to 8-9 cm
Deceleration phase – the phase in which progression slows down from 9-10 cm (fully dilated).

The labour stages and Friedman’s curve

Labour is usually classified into first stage, second stage and third stage, and timings that are applied to all women. However recent research has discovered this reasoning is now obsolete.

The three stages of the labour process are defined as follows:

First stage – the cervix dilates from 0-10 cm (this includes the latent and active phase)
Second stage – the pushing phase and the birth of your baby
Third stage – the time from the birth of your baby to the birth of the placenta and membranes.

Friedman’s graph showed the average rate of cervical dilation was about 1 centimetre per hour. The rate of dilation varied within the total time of labour but was broken into the following sections:

The average length of time it took to dilate from 0 cm to 4 cm was 8.6 hours
From 4 cm to 10 cm the average dilation time was about 5 hours. As labour appeared to speed up after 4 cm, this was considered to be the active phase of labour
When dilation reached 9 cm, there was a slight slowing down until 10 cm was reached
Pushing (second stage) took an average of 1 hour.

What is the pelvic division phase?

What we know today as the second stage of labour – the period from full dilation to the movement and birth of the baby through the birth canal – was described by Friedman as the pelvic division phase. In women who have not birthed a baby before, the second stage can take up to three hours; for women who have had a baby before (multiparous women), the second stage of labour usually doesn’t last more than 2 hours.

However, there are a number of other factors that can affect the length of the second stage:

Size and position of the baby
Gestational age
Pelvic shape
Maternal birthing position
Analgesia in labour
Strength of contractions
Previous birth history.

‘Failure to progress’ and c-section

‘Failure to progress’, also known as labour dystocia, is diagnosed when a health care provider deems labour is not progressing at the expected rate, or as quickly as it ‘should’. Failure to progress is the leading cause of unplanned cesarean births in low risk mothers, and is the most common reason for primary cesarean birth.

New research, however, suggests that some healthcare professionals might be intervening too soon, resulting in preventable intervention or surgery. Awareness of new recommendations and research will help practitioners guide their practice, and will help support a woman’s normal physiology, reducing rates of unnecessary intervention.

What are partograms and why are they used?

Based on the findings of Friedman’s study, the World Health Organization (WHO) created a partogram (also known as a partograph) to access deviations from physiological labour progress.

The partogram, which is a graphic analysis of key data plotted against time, was used in labour to access labour progression. Care providers will often use a partogram as a way to record key events in labour in an easy-to-view pictorial format, as a way to detect more easily when labour is progressing slowly.

The effective use of the partogram can save mothers’ and babies’ lives by ensuring labour is closely monitored and that potentially life threatening complications, such as obstructed labour, are detected and treated early.

You might find, or you might have seen a version of the partogram in your medical records.

How is the Friedmans curve applied during labour?

The Friedman curve is one of the first pieces of obstetric knowledge maternity care providers learn.

When a woman comes into hospital in spontaneous labour, she is usually required to have a vaginal examination, to check cervical dilation and confirm that she is in active labour (4 cm dilation or more). If her cervix is not dilated 4 cm or more, she is often encouraged to go home until contractions pick up and intensify. This part of the labour process (between 0-4 cm dilated) is referred to as the latent phase or early labour.

After being admitted to the maternity ward, the woman is then expected to dilate an average 1 cm per hour. Most hospitals have a policy of routine vaginal examinations every 3-4 hours, to check progress. A dilation rate of less than 1 cm per hour is considered abnormal and labelled a ‘failure to progress’.

More monitoring is likely to be suggested and, depending on how baby is coping, augmentation might be offered. This could involve breaking the waters if they are already intact, or administering artificial oxytocin augmentation via a drip, to speed up the contractions. It isn’t surprising that a cascade of intervention, such as epidural analgesia or continuous electronic monitoring, might begin at this stage.

The mother is likely to have continuous fetal monitoring belts attached and will be unable to move freely, limiting her ability to manage her contractions. This can make the labour process more difficult for her to manage and she is therefore more likely to request further pain relief.

A lack of maternal movement, which is common with restrictions due to continuous fetal monitoring, or because of epidural analgesia, makes it more likely that the baby is unable to get into an optimal birth position, or begins to show signs of distress. By this time, it’s very likely the mother is also feeling stressed and tired.

Her body begins to respond by releasing adrenaline. This works against her body’s natural oxytocin, which is needed for efficient uterine contractions. A reduced oxytocin level will result in a reduced pattern of labour contractions, prolonging labour progress in the first stage. Labour might appear to slow or stall, causing care providers to intervene further, to bring back uterine contractions.

Failure to progress is responsible for around 30% of all cesarean deliveries performed on first time mothers; this procedure is also known as a primary cesarean delivery.

Is Friedmans curve relevant today?

Friedman’s study was conducted nearly 70 years ago. The average age of the women Dr Friedman studied was 20; more than 95% of the women were sedated during labour, as it was the era of ‘twilight sleep’. More than 50% of the women had forceps assisted delivery and around 14% were induced or had their labour augmented with artificial oxytocin (Pitocin or Syntocinon).

These factors have the potential to change the pace of labour outside a woman’s normal and individual dilation pattern.

Since the 1950s, labour practices, and women, have changed. Women are no longer routinely sedated during labour and epidurals are much more common. Updated research suggests that it takes women much longer to dilate than previously thought, based on the Friedman curve.

To learn more about birth during Friedman’s era, read our article Childbirth Across The Last Century.

Birth in the 21st century

Giving birth today is generally considered safe, but there are significant differences between childbirth in the 1950s and our maternity care systems today. Experts are concerned at the increasing levels of medical intervention. Modern childbirth practices have changed greatly over the years and so have our bodies.

Compared with the 1950s, we have a rising maternal age and BMI rates, which create more complexities in women’s health. Women today are more likely to have risk factors for medical conditions, such as gestational diabetes, or blood pressure problems, and babies might be born at an earlier gestational age, which affects neonatal outcomes. Artificial oxytocin for labour induction and augmentation, and epidurals for pain relief, are now also commonly used. Operative ‘delivery’ in the form of forceps, however, is now less common. The average age for women having their first baby today is much closer to 30 than 20, as it was in Friedman’s study.

All of these factors are known to affect the duration of labour.

A great deal has changed, yet the same expectation of cervical dilation is applied, which is unrealistic.

Is labour longer today and why?

Labour today might be longer, due to a number of other lifestyle factors – for example:

Leading an less active lifestyle. Less physical activity in our day to day lives due to frequent use of cars instead of walking and a more sedentary lifestyle can lead to a less than optimal fetal position
Less manual labour. Use of modern technology, machinery and devices means that many of us work from computers more than ever before. This again, might lead to poor fetal positioning
Changes in diet and nutrition. Convenience foods, fast foods and changes to commercial farming practices over the years could have contributed to poorer overall health making us more prone to disease, illness and co-morbidities
Increasing maternal age. Changes to the average age a mother has her first baby might also contribute to various pregnancy or labour complications.

Zhang labour curve

A study in 2002, by Zhang and his colleagues, showed the Friedmans curve is an inaccurate description of normal labour progression in modern childbirth. It is potentially the cause of unnecessary medical intervention for a great number of women and their babies.

Not only is the overuse of medical intervention potentially harmful to mothers and their babies, it also continues to widen the health equity gap between high and low resource settings.

A large study in 2010 looked at the labour records of nearly 62,500 women from 19 hospitals across the US and contemporary patterns in their labour progress.

Women were only included in the sample if they fit the following criteria:

Women who gave birth vaginally
At full term
To a singleton baby
In a fetal head down position
Where the baby was born healthy
And labour started spontaneously.

Within this sample, most women had some form of intervention. Around 80% had epidural analgesia and about half had their labour augmented in some way.

The research found a wide variation in cervical dilation, and that the average labour was much longer than those in Friedman’s original research. On average, women began active labour at 6 cm, instead of 4 cm, as Dr Friedman reported in 1955. The average time it took to dilate during active labour (from 6 cm) was about 30 minutes for each centimetre. Around 95% of women took less than 2 hours to dilate 1 cm during active labour.

Fifteen years of research has shown the average rate of cervical dilation accelerates after 6 cm rather than at 4 cm.

Intrapartum care recommendations

In 2018, the WHO released its new intrapartum care recommendations: Intrapartum care for a positive childbirth experience. These new guidelines addressed the flaws in the Friedman curve and combined newer data to ensure evidence-based care was at the forefront of maternity care around the world.

The new recommendations consider the latent phase of labour up to 5 cm, and the active phase from 5 cm onwards. It is thought that active labour for primiparous women (women having their first baby) should not exceed 12 hours, and for multiparous women (women who have had a baby before) should not exceed 10 hours. It concluded that interventions to accelerate labour progression should not be applied before active phase (5 cm), unless clinically indicated.

During the second stage, women should be encouraged to follow their own urges to push; pushing is usually completed within 3 hours for first labours and 2 hours for subsequent births.

A new addition to these recommendations was an acknowledgement that a woman’s birth experience was a critical element in ensuring high quality care. A positive birth experience is considered one that involves a sense of personal achievement, control, involvement and choice.

To learn more about the new WHO intrapartum recommendations, read our article Don’t Speed Up Labour | Using The Friedman’s Curve.

Summary

Care providers who are aware of this newer research, and don’t intervene before 5-6 cm of dilation, will limit the use of unnecessary interventions and potentially reduce the number of c-sections occurring as a result.

When choosing care providers, find out how they base cervical dilation, and whether they are aware of the more recent research showing a slower rate of dilation up to 6 cm.

Choosing your care provider carefully will help avoid unnecessary interventions.

Recommended Reading: