Friedman’s Curve and Failure to Progress: A Leading Cause of Unplanned Cesareans
Updated on May 25, 2022 by Rebecca Dekker PhD, RN, Ihotu Ali, MPH, & Erin Wilson, MPH. Updated in 2017 by Rebecca Dekker PhD, RN & Anna Bertone, MPH. Originally published on August 28, 2013.
Friedman’s Curve and Failure to Progress: A Leading Cause of Unplanned Cesareans
Have you ever heard someone say, “My pelvis was too small” or “I was diagnosed with Failure to Progress?”
The language of childbirth is filled with paternalistic terms that indicate the power differential between doctors and pregnant families, as well as the supposed inferiority of our bodies. The physician “delivers” the baby, birthing people are “not allowed” to eat or walk untethered during labor, our labors “fail to progress” or “stall,” our pelvises are “insufficient,” our pushing efforts are “inadequate,” we’re “too short” or “too fat”, or our babies are “too big” to birth vaginally.
The purpose of this newly revised Evidence Based Birth® Signature Article is to debunk myths about labor progress and pelvic shape, and to share evidence-based information about the variations of labor progress. What lengths of labor are normal? What factors can influence the length of labor? And what are true signs that intervention is needed?
In this article, we will answer these questions, along with reviewing the history of Friedman’s Curve and the research that led to new timelines for “normal” labor. We will also discuss other methods used to assess labor progress, and how lots of factors, including fetal positioning, mobility of the pelvis, and racism, can play a role in the diagnosis of Failure to Progress. What is Failure to Progress, and how common is it?
What is Failure to Progress, and how common is it?
Failure to Progress is diagnosed when a healthcare provider states that labor is not progressing as quickly as they think it should. As you can imagine, this diagnosis can be very subjective—different providers have different ideas of how long is “too long”, and some providers are more patient (or impatient!) than others. We’ve heard many nurses and birth workers, who witness many different practice styles, refer to Failure to Progress as often being a “failure to wait”.
Around the world, and in different birth settings, there are many definitions of Failure to Progress. This vague diagnosis could mean that the dilation stage of labor is taking longer than expected; that labor has completely stopped; that the pushing stage of labor is slow; that the descent of the baby through the pelvis is slow; or that the baby’s head is not fitting through the pelvis (sometimes called cephalopelvic disproportion or CPD).
These varying interpretations mean different rates of Failure to Progress depending on which definition is being used and where a birth is taking place. For example, Failure to Progress was the cause of about 42% of Cesareans in Queensland, Australia, and 34% of Cesareans in the United Kingdom. (Nippita et al. 2015). In the United States, Failure to Progress is the most common reason for primary (first) Cesarean deliveries (Boyle et al. 2013) as well as the most common reason that people who give birth at home with midwives are transferred to the hospital (Blix et al. 2014). However, rates of Failure to Progress in planned home births are low—in a study of 16,924 planned U.S. home births, only 4% of people were transferred to the hospital for Failure to Progress (Cheyney et al. 2014). This rate is much lower than what is seen in hospital settings. According to an article published in American Family Physician in 2021, “abnormally slow or protracted labor accounts for 25% to 55% of all Cesarean deliveries” (Lefevre et al. 2021).
Another issue is that many people are inaccurately diagnosed with Failure to Progress when they’re still in early labor, or before they push the length of time that research has shown to be within the range of normal (Alrais, et al. 2019).
Overall, it’s difficult to diagnose “Failure to Progress” without a clear picture of what “normal” labor is– and the definition of normal has evolved over the years.
What is the history of Failure to Progress?
For many years, what we knew about the average length of labor was based on a graph called Friedman’s Curve—a historical artifact from the 1950s that still affects birthing people today.
In 1955, Dr. Emanuel Friedman of Columbia University published a study that described the average amount of time it takes to dilate by centimeter based on his observation of 500 white patients at a single hospital in New York City (Friedman, 1955). The graph that he created from these people giving birth for the first time (and later in a similar study with people who had given birth before (Friedman, 1956)) went on to become known around the world as “Friedman’s Curve.”
But let’s pause for a minute…do the demographics of Dr. Friedman’s study jump out to you? You may be wondering why Dr. Friedman only included white people in his study. Well, Dr. Friedman’s work took place when hospitals were still formally segregated in the U.S.—in both the North and South. At the time, Black patients were not allowed to be admitted to many hospitals. Often, they were actively blocked from access to physicians and medication, even under dire/emergency situations. Some hospitals admitted Black people in labor, but only to separate floors or wards (often the basement), where they did not have access to treatment options that white patients received under the same roof. Under these extremely challenging conditions, many Black communities resisted by setting up their own hospitals, medical schools, and clinics (Reynolds, 2004).
It was not until the mid-1960s that hospitals faced pressure to desegregate in the U.S. and, even then, hospital administrations were still resistant to desegregation. In some hospitals, they only began offering care to Black patients after the passage of Medicare, which granted federal funding solely to desegrated hospitals (the passage of this bill, by the way, was not supported by the American Medical Association) (NPR, 2015).
Today, the segregated history of U.S. healthcare has been largely erased (i.e. whitewashed) from the education of its predominantly white workforce of health care professionals. Out of curiosity, we looked for a written history of segregation at the hospital where Dr. Friedman carried out his study (New York Presbyterian Hospital, which used to be known as Sloane Memorial), but we could not find any books that mention segregation there. Their own website does not mention segregation or desegregation in their timeline.
Back to more details about Dr. Friedman’s study…What else do we know about the 500 participants in the study? Their ages ranged from 13 to 42 years old, and most (70%) were between the age of 2030. More than half had forceps used on them during delivery (55%), and only nine (1.8%) gave birth by Cesarean. There were 14 breech births (2.8%), four twin births (0.9%), and four stillbirths or newborn deaths. The babies ranged in weight from 4 lbs. 9 oz. to 10 lbs. 6 oz., with most babies falling into a normal weight range (5 lbs. 8 oz. to 8 lbs. 13 oz.). Pitocin was used to induce or augment labor in only 69 people (13.8%).
Back then, “Twilight Sleep” was common practice for white birthing patients (it was usually not offered to Black patients), and so 117 of the participants (23%) were lightly sedated, 210 (42%) were moderately sedated, and 154 (31%) were deeply (sometimes “excessively”) sedated with Demerol and Scopolamine. This means that 481 (96%) of the 500 people giving birth were sedated with drugs (Friedman, 1955).
Figure 1: Friedman's Curve ( 1955 - 1956 )
The average length of time it took for these patients to get from zero cm to four cm was 8.6 hours (±6 hours). Once they reached four cm, labor sped up—also known as “active labor”—and, at that point, they dilated a rapid average of three cm per hour (±2 cm) until reaching nine cm. At nine cm, there was a slight slowing down before patients reached ten cm. The average length of time it took to get from four cm to ten cm was 4.9 hours (±4 hours). The average length of pushing (second stage) was one hour (±0.8 hours).
Using today’s standards for research, Dr. Friedman’s study would be considered unethical because of the many invasive vaginal exams performed on sedated/sleeping patients. The sedation may have also substantially sped up labor, and the common use of mid-forceps meant that babies were often pulled out while they were still higher up in the pelvis. Also, none of the patients in Dr. Friedman’s study had epidurals, which are known to slow down the labor process (Alexander et al. 2002, Frigo et al. 2011).
Most researchers today believe we should no longer apply Friedman’s Curve to labors because too many things have changed since 1955. Epidurals are used instead of sedation; Pitocin is used much more frequently; people giving birth today are older and tend to weigh more; and forceps-assisted births are rare (Laughon et al. 2012).
Use of the Partograph in Low-Income Countries
Today, Dr. Friedman’s work lives on in the concept of a labor curve or partograph (also called a partogram or partogramme depending on the country where it is being used). While prior physicians and researchers had studied the overall length of labor, it was Dr. Friedman who introduced the concept of plotting centimeters of cervical dilation over time.
The original design of the partograph was based on the results of Dr. Friedman’s study, and both the original and a more modern version with a longer timeline are still commonly used today (Hofmeyr et al. 2021). The basic principles are the same, and data points include cervical dilation, fetal heart rate, descent of the baby’s head, and vital signs of the birthing person. An ‘alert’ line and an ‘action’ line indicate when the care provider should consider intervention or transfer to a hospital.
While evidence supporting widespread use of the partograph is mixed, it is considered by many to be an important tool for people giving birth in countries defined as “low income” according to the World Bank. Specifically, when people are laboring at long distances from hospitals, are not using electronic fetal monitoring, and have limited or no access to technology (such as anesthesia and surgery), the World Health Organization (WHO) recommends use of the partograph to assess if a labor is abnormal and could be heading down a dangerous path for the birthing person or baby. It is thought that proper use of the partograph can ensure that life-threatening complications such as obstructed labor are identified and treated (Dalal et al. 2018).
What changed in the 2010s?
In the early-to-mid 2010s, there was a public health push to lower the Cesarean rate in the U.S., and this was accompanied by some major shifts in defining normal labor. Researchers who were studying labor progress noticed that labor usually speeds up at about six centimeters (cm) of dilation (instead of at four cm as Friedman had described decades earlier). This discovery resulted in a new definition of when active labor begins: six centimeters (this is sometimes referred to by the phrase, “Six is the new four.”) New research also showed that, before someone reaches six cm dilation, it is normal for labor to progress very slowly or with no noticeable pattern (Zhang et. al 2010).
In 2014, the American Congress of Obstetricians and Gynecologists, together with the Society for Maternal Fetal Medicine, published new guidelines on labor progress. Their new “normal” length of labor is longer than Friedman’s definition, and there is more room for flexibility, such as when an epidural is being used. In addition, new timelines were developed to define when labor progress is abnormally slow—and new terms and definitions were proposed (such as the diagnosis of “labor arrest”), along with an attempted elimination of the vague label “failure to progress.”
Zhang’s Study Serves as the Basis of New Guidelines
In one important study published in 2010, researchers looked at the labor records of more than 62,000 people from 19 hospitals across the U.S. Participants were included if they gave birth vaginally at term to a single baby who was positioned head-down, if the babies were born healthy, and if the labors started spontaneously (were not medically induced). Most of the birthing people had interventions during their labors—overall, about half of them had their labors “augmented” or sped up with oxytocin (Pitocin), and 80% had epidurals (Zhang et al. 2010).
The researchers found that on average, people did not rapidly dilate starting at four cm like Dr. Friedman saw back in 1955. Instead, active labor was reached at around six cm. This was true for both people giving birth for the first time and those who had given birth before, although those who had given birth before tended to dilate faster once they reached active labor (six cm). The average time it took to dilate during active labor was about half an hour for each centimeter (and faster for those who had given birth before). The vast majority of people (95%) took less than two hours to dilate one cm during active labor.
Interestingly, researchers found that before six cm, many people (both people giving birth for the first time and those who had given birth before) went long periods without any dilation—and this was within the range of normal in the sample. For example, those laboring took an average of 1.8 hours to get from three cm to four cm, but the top 5th percentile of the sample (still in the range of normal) took as long as 8 hours. On average, people took 1.3 hours to get from four cm to five cm, but the top 5% took seven hours. Remember: all these people went on to give birth vaginally to healthy babies.
When it came to pushing, or the “second stage” of labor, first-time parents pushed for an average of 1.1 hours with an epidural and 0.6 hours without an epidural. At the very extreme end of normal, some first timers (the 5% that pushed the longest) pushed for 3.6 hours with an epidural and 2.8 hours without an epidural. Those that had given birth before had much shorter pushing phases—on average, they spent less than 30 minutes pushing with an epidural, and about 15 minutes without an epidural.
Other researchers have also confirmed that, for various reasons, including an older and heavier population and different clinical practices, labor lasts longer today than it did in Dr. Friedman’s time.
More current studies like this one show that if we continue to apply Friedman’s Curve to birthing people today, we are saying that half of all people have “abnormally” slow labors. This creates an expectation for people giving birth for the first time to dilate much faster than today’s average, and applying these standards means that many people are being diagnosed with Failure to Progress when what they are experiencing is normal.
Here is a graphical representation of some of the results from Zhang’s study:
Cervical Dialation and Pushing for the Median and the 95th Percentile in Zhang's 2010 Study
This bar graph shows the amount of time (in hours) that it took for both the middle of the study group and the slowest five percent of the study group to dilate (per centimeter) and to push. Bottom line: the fastest, middle, and slowest times are ALL versions of “normal” labor in this study group!
So, what are the current evidence-based definitions of normal and abnormal labor?
Because of all the updated research that has come out in the past ten years, the newly proposed definitions of normal and abnormal labor look quite different than the old definitions. In 2012, new definitions for normal and arrested labor were issued out of the NICHD/SMFM/ACOG workshop on preventing the first Cesarean (Spong et al. 2012). These definitions were reaffirmed in the 2014 “Preventing the Primary Cesarean” guidelines (ACOG, 2014). Table 1 shows a comparison.
Table 1: Failure to Progress, Old and New Definitions
- ACOG Committee on Practice (2003). ACOG Practice Bulletin Number 49, December 2003: Dystocia and augmentation of labor. Obstet Gynecol 102(6): 1445-1454.
- Spong et al (2012). Preventing the first cesarean delivery: summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, and American College of Obstetricians and Gynecologists Workshop.” Obstet Gynecol 120(5): 1181-1193.
- ACOG, SMFM, Caughey, A. B., et al. (2014). “Safe prevention of the primary cesarean delivery.” Am J Obstet Gynecol 210:179-193.
- ACOG Committee on Practice (2009). ACOG Practice Bulletin No. 107: Induction of labor. Obstet Gynecol 114(2 Pt 1): 386-397.
With the new guidelines eliminating the diagnosis of Failure to Progress, did things get better?
In 2013, before the new guidelines were released, researchers published a report about 38,484 people who had their first Cesarean (primary Cesarean) in the U.S. during a six-year period. The overall primary Cesarean rate in the study was 21.3%, and the Cesarean rate among people giving birth for the first time was 30.8%. One-third (35%) of the primary Cesareans in the overall sample were due to a diagnosis of “Failure to Progress,” or slow progress in labor. Nearly half (41.3%) of the Cesareans in people giving birth for the first time were due to Failure to Progress. This means that from 2002 to 2008, approximately one in ten (13%) of all people giving birth for the first time in the U.S. had a Cesarean for Failure to Progress (Boyle et al. 2013).
Research from the U.S.:
In 2018, after the new guidelines came out, researchers published a study investigating whether the new “Safe Prevention of the Primary Cesarean” guidelines were being followed by physicians at a single academic medical center in the U.S. (Alrais et al. 2019). They found that, of the Cesareans that occurred because of a “Failure to Progress” diagnosis during the year-long study period, over half did not meet the criteria from the new guidelines.
Even more troubling, the research showed that care providers were less likely to follow the updated guidelines if they were attending a weekend versus a weekday birth (possibly because they did not want to be at the hospital on a weekend). In the Cesarean births where the new, longer definitions of labor arrest were used, there was no increase in adverse outcomes for the birthing person or baby. In other words, at this hospital, there were no major safety issues with using new guidelines that allow for longer labors.
Research from Italy:
In 2016, researchers in Italy enrolled 419 patients in a prospective study in which half of the participants had standard care based on Friedman’s Curve, and the other half were given a new model of care that followed the ACOG/SMFM’s new consensus guidelines. People could be included in the study if they were giving birth for the first time and were pregnant with a single baby in head-first position. They could be in spontaneous labor at term or having an induced labor post-term (Ragusa et al. 2016).
With the old care model, not only was Friedman’s Curve used to define normal and abnormal labor, but food was banned, and laboring people were usually restricted to bed and told to push on their backs. With the new care model, Friedman’s Curve was used as a screening tool, but providers were instructed to have more patience with labor and carry out further assessments before they decided on surgery or medical intervention. In addition, laboring people who had the new model of care were encouraged to walk during labor and to push and give birth in the position they found most comfortable. They were also given free access to food and drink and the care providers used a standardized protocol to diagnose fetal distress.
Birthing people who received the old model of care (strict adherence to Friedman’s Curve) had a Cesarean rate more than twice as high as those in the new model of care group: 22.2% vs. 10.3%. Those in the new model of care group also had fewer interventions overall including Pitocin augmentation or having their water artificially broken. The percentage of newborns with low Apgar scores or low umbilical cord pH was higher in the old model of care group (2.3% vs. 0.5%). The average length of labor was the same in both groups. In summary, the old model of care group had more interventions with almost the same outcomes.
Dr. Friedman Continues to Defend the Curve
Despite a large consensus that it is time to use new definitions, Dr. Friedman, who is still publishing, continues to adamantly defend the use of Friedman’s Curve. As part of his criticism of the new guidelines, Dr. Friedman made the point that overall Cesarean rates in the U.S. have not come down after the new guidelines were published.
It is true that a huge rise in Cesarean rates in the U.S. occurred between 1976-2007. The Cesarean rate eventually plateaued at around one in three in 2007 and has remained stable since that time (Sakala et al. 2020). The U.S. Cesarean rate continues to hover around 32-33%, despite the new guidelines that were supposed to help lower the Cesarean rate (Cohen and Friedman, 2020).
However, the lack in change of Cesarean rates from 2007 to present could be because, as we have seen, many providers have not truly adopted the new guidelines yet. It’s also possible that any potential decline in the Cesarean rate due to the new guidelines may be balanced out by an increase in Cesarean rates from other causes.
What can make labor move faster or more slowly?
As we have seen in the research covered so far, it is not easy to apply a specific curve or timeline to all labors and births, because each person has unique factors that can lengthen or shorten their labor.
May lengthen labor:
- Epidural use may lengthen both labor (Alexander et al. 2002, Frigo et al. 2011) and pushing (AnimSomuah et al. 2011)
- Heavy sedation (Friedman 1955)
- Being overweight or obese (Kominiarek et al. 2011; Carlhall 2013; Kawakita et al. 2016)
- Advanced maternal age (Sheiner et al. 2002a; Timofeev 2013)
- Having labor medically induced (Sheiner et al. 2002a) (Vahratian et al. 2005)
- Giving birth for the first time (Zhang, Landy et al. 2010), (Sheiner et al. 2002a)
- Posterior positioning of the baby (i.e. OP, sunny-side up) (Gardberg & Tuppurainen 1994, Senecal et al. 2005)
- Baby’s head is tilted sideways (i.e. asynclitic) (Malvasi 2015)
- Being confined to a bed (Lawrence et al. 2013)
- Dehydration (Dawood et al. 2013)
- Being a survivor of sexual assault (Nerum et al. 2010)
- Giving birth to twins (Leftwich et al. 2013)
- Premature rupture of the membranes (PROM, sac of water releases before labor begins) (Sheiner et al. 2002a)
- Being pregnant with a big baby (Sheiner et al. 2002b)
- Maternal health problems such as gestational diabetes, hypertension or preeclampsia, low amniotic fluid or high amniotic fluid levels, having had a previous infant die during or shortly after labor, and infertility treatment (Sheiner, Levy et al. 2002a; Sheiner et al. 2002b)
- Having a successful external cephalic version for a breech baby (Basu et al. 2016)
- Having been diagnosed with Failure to Progress in a previous birth (Tobias et al. 2015)
May shorten labor:
- Not having an epidural during labor (Alexander et al. 2002, Frigo et al. 2011) and pushing (AnimSomuah et al. 2011)
- Pitocin augmentation/acceleration (Bugg et al. 2013)
- Having given birth before (Zhang, Landy et al. 2010; Sheiner et al. 2002a)
- Upright positions— during labor (Lawrence et al. 2013) and pushing (Gupta et al. 2012)
- Baby’s head is “engaged” in the pelvis and pressing directly on the cervix (Moberg, 2014)
- Doula support (Bohren et al. 2017)
- Pelvic mobility (Dehghan et al. 2014) (Calais-Germain, 2003)
May lengthen or shorten labor, or may not change anything at all:
- Artificially breaking the waters (AROM) (Friedman 1955; Smyth et al. 2013)
- Size and shape of the birthing person’s pelvis (Haeusler et al. 2021)
Can the size or shape of someone’s pelvis influence the way they labor?
You can think of labor like a negotiation or dance between baby and pelvis. There are many factors that influence how a baby and pelvis ‘fit’ together and the ease with which a baby can move through a pelvis.
These factors include but are not limited to:
- Mobility of the pelvis (Dehgan, 2014, Calais-Germain, 2003)
- Position of the laboring person (upright, laying down, side-lying, etc.) (Lawrence et al. 2013, Gupta et al. 2012)
- Position of the baby in relation to the pelvis (Gardberg & Tuppurainen 1994, Senecal et al. 2005, Malvasi 2015)
- Whether baby’s head is “engaged” or sitting on top of the cervix (Moberg, 2014)
- The cascade of hormones at play in labor (Dehghan et al. 2014)
There can be a big difference in the labor of someone who is upright and using an open pelvis position (for example, sitting on a birthing ball while leaning forward) as compared to someone who is laboring in bed with their pelvis and sacrum (i.e. tailbone) in a more closed position. In fact, through computational modeling, researchers have found that pelvic outlet diameters in pregnant people can increase by 6.1mm from front-to-back and 11mm from side-to-side when a pregnant person is squatting (Hemmerich et al. 2019).
Many people think of the pelvis as solid and inflexible, but the pelvis is a complex of three joints (two sacroiliac joints and the pubic symphysis) that can shift and open slightly. This is particularly true because the hormone relaxin, released during pregnancy and labor, softens the ligaments and connective tissues, allowing the pelvis to have even more mobility and flexibility. This helps to further widen the diameter of the pelvic inlet and outlet spaces that make up the birth canal, and makes more room for the baby to come down and out (Dehghan et al. 2014).
A birthing person’s emotional state can also impact the way their pelvis opens (or does not open) in birth. For example, a past experience of trauma, not feeling safe in their birthing space, experiencing microaggressions during labor, or experiencing a fight or flight response can cause a nervous system reaction that negatively impacts pelvic mobility. The psoas muscle, which attaches to the spine and helps us stand and walk upright, helps with this type of subconscious regulation in our bodies. Integrative and Indigenous healers and bodyworkers often refer to the psoas as the soul muscle for its perceptive, bio-intelligent properties (Menakem, 2022).
Why are so many people told that their babies cannot “fit” through their pelvis?
For many years of human history, diseases like scurvy and rickets were widespread. Scurvy and rickets are caused by deficiencies in diet and thus a lack of essential nutrients (vitamin C and D), so they inhibit proper bone development. These differences are not genetic or due to differing pelvic shapes, but due to lack of access to nutritious foods to eat, especially during childhood when your bones are growing. Thus, for a long time, severe pelvic malformations made it impossible for some babies to be born vaginally.
Historical ideas about “racial” pelvic shapes also influenced peoples’ beliefs about the concept of a baby not fitting through a pelvis. In the late 1800s and early 1900s, pelvic structure was a marker of hereditary worth and having a small pelvic cavity was thought of as a sign of “biological inferiority” according to some physicians (O’Brien, 2013). Horrifically, forced (and in some cases secret) sterilizations were performed on certain Indigenous people in Mexico, with the idea that they should not be allowed to give birth due to their smaller stature.
In the 1930s, and updated in the 1940s, the Caldwell-Moloy classification system introduced the concept of four different categories of pelvic shape (Caldwell and Moloy, 1938). The categories were defined as:
- Gynaecoid-This translates to “woman type” in Greek and, according to the authors, is the most ideal/”normal” shape to have. It is characterized by a round or slightly oval shaped pelvic brim with a wide sub-pubic arch and a sacrum tilted toward the back of the body (posterior).
- Android-This translates to “man type” in Greek. It has the widest front-to-back diameter at the brim-closer to the sacrum (back) than the pubis (front). The sacrum is tilted toward the front of the body (anterior), and the pelvic cavity is widest at the top and most narrow at the bottom (also called funnel-shaped).
- Anthropoid-This translates to “human-like” in Greek, and was used to refer to animals similar to humans, or considered “ape-like” and inferior for giving birth. The shape is thought to be longer, narrower, and more oval than other categories, and was often assigned by physicians to women of African descent.
- Platypelloid-This translates to “flat type” and is significantly wider side-to-side than front to back.
Some of the more obvious racial and gender stereotypes are now left out of medical textbooks (such as the reference to the word “ape”), but the theory of distinct pelvis shapes has carried on for decades, uninvestigated and unquestioned.
In 2015, an Australian study sought to re-test the accuracy of Caldwell-Moloy’s classifications of the four shapes (Kuliukas et al. 2015). They took CT scans of 64 randomly selected, consenting people who identified as women, and plotted their pelvic characteristics on a graph to see if they clustered into categories resembling the four pelvis shapes.
However, instead of clustering in distinct “types” or “categories,” the data were equally spread across what the authors call a “nebulous cloud of variation,” with many pelvises representing combinations, such as gynecoid posterior pelvis with an android fore-pelvis. Rather than trying to determine pelvic shape or making assumptions based on someone’s body-type, race or gender expression, the researchers recommend considering pelvic inlet, outlet, and mid-pelvis characteristics as just one of a long list of factors that can influence labor.
What is pelvimetry?
Today, pelvimetry may be used to determine the size and shape of a birthing person’s pelvis. In theory, pelvimetry is supposed to help doctors to determine if a particular pregnant person will “be able” to give birth vaginally. The idea is that, by measuring a pregnant person’s pelvis, care providers may be able to prevent unnecessary emergent Cesareans by determining before labor if it is likely that a baby “cannot fit” through a pelvis.
If a care provider determines that the size of the baby and the size of the pelvis are not a good fit (called a cephalopelvic disproportion or CPD), then a Cesarean delivery could be planned. The rationale of this approach is that a planned Cesarean delivery carries less risk overall for the birthing person and baby than an urgent Cesarean that could occur if a CPD is diagnosed in labor.
Pelvimetry can be done through a physical assessment in which the care provider does a vaginal exam and feels the various pelvic bones for placement and shape. It can also be done through imaging such as an x-ray or MRI. These different methods carry varying risks-a physical exam may be extremely uncomfortable for the birthing person; an x-ray may expose the baby to dangerous radiation; and an MRI is too costly to be used as regular screening tool. Since rickets and scurvy are mostly diseases of the past, and true pelvic malformation is extremely rare, it’s questionable whether screening all pregnant people is more helpful or harmful. In most cases, this is not standard protocol.
Evidence on Pelvimetry
In a Cochrane review from 2017, researchers combined the results of five studies on pelvimetry (Pattinson, et al. 2017). Each trial had a slightly different design, but the researchers’ overall goal was to see if measuring pelvises in pregnancy could help prevent emergent Cesareans. Pregnant people could be included if their baby was in a head-down position, and they were at or near term.
The results of these trials are considered low quality or very low quality because blinding of the pregnant person and care providers was not possible in their design, which means there is the potential for bias.
In total, records of pelvimetry studies from 1,159 pregnant people were reviewed. In these trials, X-ray was the only type of imaging used. The patients who had X-ray pelvimetry were compared to the patients who did not have X-rays. The no X-ray group was made up of patients who had a clinical pelvimetry exam (defined as a physical exam) or no pelvimetry exam. There were no trials that compared clinical pelvimetry exams to not having a pelvimetry exam. There were also no trials that assessed other imaging methods such as MRI or CT scan.
In these 5 trials, pregnant people who had an X-ray exam to measure their pelvis (X-ray pelvimetry) were 34% more likely to have a Cesarean delivery than pregnant people who had a physical exam or no pelvimetry assessment. There were no significant differences in health outcomes for birthing people or babies between the two groups. The authors concluded that patients who had X-ray pelvimetry exams were more likely to have Cesarean deliveries and that, because there was no improvement in health outcomes, there are not significant data to support the use of X-ray pelvimetry exams in all pregnant people. The authors encourage further studies in this area to determine if there is a useful purpose for pelvimetry studies in some specific situations. However, it’s important to note that X-rays of the pelvis during pregnancy are almost never used today because of the known harms of radiation on the pregnant person and fetus.
Is it harmful to have a labor with a long first stage? What are the risks to birthing people and babies?
Research on long labors in people giving birth for the first time:
In one study, researchers looked at 10,000 people giving birth for the first time at a single hospital between 1990 and 2008 in the U.S. (Cheng et al. 2010). They excluded all people who had Cesareans for fetal distress from this study, so none of the babies were diagnosed with fetal distress before birth. Babies who were born after a first stage of labor that took longer than 30 hours (the top 5th percentile, or the longest 5% in the sample) were more likely to be admitted to the neonatal intensive care unit (NICU) compared to the labors in the 5th to 95th percentiles (9.8% vs. 4.7%). However, there was no other relationship between long labors and other poor newborn outcomes—including Apgar scores, umbilical cord pH, meconium aspiration, infection, shoulder dystocia, or birth trauma.
Birthing people with the longest labors were more likely to have an infection of the uterus (23.5% vs. 12.5%) and to have a Cesarean (13.5% vs. 6.1%), but there was no increase in the risk of postpartum hemorrhage. The authors did not describe the number of vaginal exams that participants received, which is important, because a higher number of vaginal exams could have contributed to higher infection rates among the people with long labors. (For more information about the risk of vaginal exams after the waters have broken, see the Evidence Based Birth® article on PROM).
Research on long labors in people who have given birth before:
A second study focused on varying lengths of labor in people who had given birth before (i.e. people who are “multiparous”) at 7 hospitals in the Northeast U.S. (Wang et al. 2020). In this study, researchers looked back in time at the medical records of multiparous birthing people who were pregnant with a single baby in head-first position, and who planned on a vaginal delivery. There were 7,109 participants in the study. The length of labor was divided into first and second stages and further separated into categories as follows: less than 6 hours, 6-11.9 hours, 12-17.9 hours, 18-23.9 hours, and 24 hours and over. The start of labor was defined as the onset of regular, painful contractions.
Researchers looked at adverse outcomes in both birthing people and their babies to see if there were any trends related to the length of labor. For birthing people, there was no association between the length of the first stage of labor and Cesarean delivery or postpartum hemorrhage.
There was an increased risk of two outcomes with a longer first stage of labor—instrumental deliveries and severe tears. Instrumental deliveries are a known risk factor for more severe tearing, so let’s look at those numbers more closely:
- The study group with labors under 6 hours had instrumental deliveries at a rate of 2.3%.
- Those with labors between 12 and 17 hours had an instrumental delivery rate of 4.3%, and those with labors over 24 hours had an instrumental delivery rate of 7.3%.
- It follows that severe tearing rates would increase in people who had instrumental deliveries—and this rate did increase, though not as dramatically.
- In those with labors under 6 hours, 1.1% experienced severe tearing, and in those with labors over 24 hours, 2.3% experienced severe tearing.
- So, not all the people with instrumental deliveries had severe tearing. Because there were no other recorded complications in the people who had long labors, it’s not clear why they had more instrumental deliveries.
In babies who experienced longer labor in this study, there were not increases in any of the measured health outcomes which included shoulder dystocia, Apgar scores below 7, neonatal resuscitation, and assisted ventilation. In fact, the babies with the highest rate of transfer to the NICU were the babies in the shortest labor group (4.6% in the longest labor group vs. 5.4-7.0% in the other, shorter labor groups).
Qualitative research about long labors:
The third study we reviewed is different from the others because there is a qualitative component— meaning that there are open-ended questions to describe the experiences of the people who gave birth (Gaudernack et al. 2020). In this study, researchers in Norway looked at the effect of labor duration on birth experience. A questionnaire was sent to people who gave birth for the first time at a university hospital during the study period from late 2012 to late 2014. Birthing people were eligible to be included in the study (and thus received a questionnaire in the mail) if they were full term and pregnant with one baby in the head-first position at the time of their hospital admission. Those who gave birth by elective Cesarean were excluded. Most (71%) of eligible participants responded to the questionnaire, for a total of 459 participants.
In this study, a “long” labor was defined as a first stage of labor over 12 hours. Those with labors over 12 hours had lower scores in two self-reported categories: “own capacity” and “perceived safety.” Birthing people who labored for more than 12 hours were also more likely to disagree with the statement “Labor and birth went as a I expected”.
One of the authors’ hypotheses was that a longer labor could increase patients’ ideas about electing for a Cesarean delivery in subsequent pregnancies, but this did not turn out to be the case. The only two scenarios that increased wishes for a Cesarean delivery in future pregnancies were operative delivery (using a vacuum or forceps) and intrapartum (unplanned) Cesarean delivery. The factors most associated with negative feelings about labor in this study were induction, postpartum hemorrhage, and operative delivery.
In terms of health outcomes and interventions, there were some notable differences between the 12+ hour labor group and the 12 hours or less group. The 12+ hour labor group had almost double the rate of Pitocin augmentation (98.8% versus 55%) and use of epidurals (96.5% vs. 58.4%). Epidurals are more common when Pitocin is used, so it could be that the “longer” labor caused the care provider to order Pitocin to speed things up, which in turn made contractions more painful and caused more birthing people to request epidurals.
The 12+ hour labor group also had more unplanned Cesareans (21.2% vs. 8.3%), more operative vaginal births (37.6% vs. 22%), and more cases of postpartum bleeding >500mL (38.8% vs. 20.4%). Because health outcomes for birthing people and babies were not collected in this study, it is not clear if the increase in Cesareans and operative vaginal deliveries were the result of complications or simply time management tools. In addition, heavier postpartum bleeding is more common with Cesareans and instrumental deliveries. So, again, it is not clear if the additional bleeding was the result of the “long” labors themselves or because of the increased use of Cesareans and instrumental deliveries with longer labors.
The researchers point out that the questionnaire they used did not have specific questions about the early phase of labor and that participants’ ideas about labor and birth “going as expected” were impacted by their expectations and knowledge of what labor would be like. Another important note on this research is the rate of interventions. The overall induction rate was about 25% (lower than what we see in a lot of birth settings), and the operative vaginal delivery rate was 25% (much higher than what we see in most birth settings). Also important: active labor in this hospital was defined as 5cm, which is not in line with the older or current guidelines (4cm and 6cm, respectively), and may have caused some unnecessary diagnoses of long labor.
What about Failed Inductions of labor? How is this diagnosed?
In the past, there was no consensus in the medical community on what criteria made up a “failed induction.” However, the question of how to define or diagnose a failed induction is important, because more than four out of ten people giving birth for the first time in the U.S. have their labors medically induced (Laughon et al. 2012).
Although researchers have found that elective inductions don’t increase the Cesarean rate in controlled study conditions (Grobman et al. 2018), other researchers have looked at real-world settings and found substantial rises in Cesarean rates when induction is compared to spontaneous labor (ACOG, 2019).
As with the general guidelines on labor progress, guidelines for induction management have evolved to be more flexible and longer with the aim of reducing unplanned Cesarean births.
Current ACOG guidelines on induction:
In their 2009 guidelines on elective induction, ACOG recommended at least 12 to 18 hours of latent (early) labor before a diagnosis of failed induction (ACOG, 2009). But in their 2014 consensus guidelines, a new and longer definition was proposed. The current ACOG guidelines, which were reaffirmed in 2019, state that, if the health of the baby and birthing person allow, Cesarean deliveries for failed induction should be avoided unless the latent phase of labor is at least 24 hours and oxytocin (Pitocin) has been administered for 12-18 hours after membrane rupture. The above timeline does not include cervical ripening, which is recommended in the guideline for those with an unfavorable cervix as multiple studies have proven that it lowers the rate of unplanned Cesareans (ACOG, 2019).
What other factors play a role in Failure to Progress Diagnoses?
A summary statement from the 2012 NICHD/SMFM/ACOG joint workshop on preventing the first Cesarean declared that non-medical factors also play an important role in Cesareans that are performed for Failure to Progress:
Time limits, labor and delivery scheduling issues, operating room staff availability, and limited space and resources to support long labors and inductions are all factors that encourage providers to label (or mislabel) a person’s labor as Failure to Progress. Other factors that lead to an overabundance of Failure to Progress diagnoses include care provider fatigue, high workload, and sleep deprivation. In addition, evidence has shown that Cesarean rates for Failure to Progress go up when the care provider knows that they can go to sleep, or when they could be doing office hours instead of participating in a long labor and vaginal birth (Klasko et al. 1995, Spetz et al. 2001, Spong et al. 2012).
The workshop summary also stated that there are financial incentives to diagnosing Failure to Progress:
“Financial incentives and disincentives related to work efficiency and staffing workload may also tilt the scale toward more liberal performance of scheduled Cesarean deliveries. Given the time required to monitor a complicated labor, there is a financial disincentive to persevere when labor does not proceed efficiently or if borderline fetal heart patterns are present. Evidence suggests that doctors who are salaried and participate in profit sharing, thus reducing the financial incentive to limit the time spent managing labor, have lower Cesarean rates.”
To stop over-diagnoses of “Failure to Progress,” the following recommendations were made:
- Care providers should stick to proper, current definitions of labor arrest, and avoid using the vague term “Failure to Progress” (see Table 1 for definitions)
- Birthing people should be given adequate time for both labor and pushing—and “adequate” time is much longer than what has traditionally been “allowed” in the past
- Inductions should only be labeled “failed” after at least 24 hours of Pitocin (plus water broken, if possible)—this clock should not start until after cervical ripening, if necessary, is completed
- Birthing people—particularly those giving birth for the first time—with an unripe cervix should not be induced unless the induction is medically necessary
- Each care provider should receive feedback from their hospital on how often they improperly diagnose labor arrest or “failed induction”
If someone is diagnosed with Failure to Progress, are there any other options beside Cesarean?
First, it is important that the proper definitions for “labor arrest” are used (see the Table 1). Evidence suggests that if a person is in normal labor (not induced), and if they are less than six cm when their labor has stalled, then this is not true “labor arrest” and they should simply receive supportive care.
Supportive care may mean continued observation, Pitocin augmentation if needed, or discharge from the hospital (discharge is recommended if labor has stopped, water is intact, and birthing person and baby are both in good condition). If first-stage labor arrest is diagnosed after the birthing person has reached at least six cm, medical options include breaking the water, Pitocin augmentation, and/ or allowing the person to continue to labor, as long as both the birthing person and baby are healthy (Spong et al., 2013; Shields et al., 2007). Obviously, there will be cases of labor arrest where a Cesarean becomes necessary.
Based on a thorough review of the evidence, authors Goer and Romano suggested using four preventive “P’s” to deal with some outside factors that may cause labor to slow down in the first place (Goer and Romano, 2012). These “P’s” include:
Permission: Give the laboring person permission to move about, eat and drink when they want to, and use whatever positions they find comfortable. Natural behaviors should not be restricted “unless there is a compelling medical need to do so and the person has made an informed choice to comply with the recommended restrictions” (p. 182).
Physical environment: The birthing space should be large enough for the laboring person and their support team. There should be private places to walk, tubs and showers for water therapy, and birth balls and other props that encourage upright positioning. The laboring person should have a say in the physical aspects of their environment, including lighting, sound, and the people who come in and out of the room.
Practices: Practices that restrict mobility—such as being hooked up to continuous electronic fetal monitoring or IV fluids—should not be used unless medically necessary. If these practices become necessary, care providers should try to lessen their impact on the laboring person’s mobility. For example, portable electronic monitors could be used so that the laboring person can remain mobile, instead of requiring them to lie in bed; or a peanut ball could be used to help position a person with an epidural.
People: Care providers should be supportive, nonjudgmental, and respect the birthing person’s autonomy. Birthing people should feel free to express their emotions or needs “without fear of being judged or pressure to comply with staff preferences or expectations” (p. 183).
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We would like to extend our gratitude to our expert clinician reviewers for their feedback: Vincenzo Berghella MD, Professor and Director, Division of Maternal-Fetal Medicine at Jefferson University; Shannon J. Voogt, MD, Board-Certified in Family Medicine; Angela Reidner CNM, Illinois Valley Community Hospital; and Steve Calvin MD, an OB /GYN specializing in Maternal- Fetal Medicine, an Associate Clinical Professor at the University of Minnesota, and the medical director of the Minnesota Birth Center, for their valuable feedback and critique of this article before publication.
We would also like to thank Cristen Pascucci and Sharon Muza CD(DONA), BDT(DONA), LCCE, FACCE, for their medical editing assistance.
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