Pregnant women know a thing or two about curves. But, beyond the unmistakable silhouette of a mother-to-be, the curve that may have defined modern childbirth more than any other is on a graph developed in the 1950s by an American physician named Emmanuel Friedman, MD. Today, scientists have challenged Friedman’s curve, which charts the progress of what was considered normal labor.

A convincing body of evidence shows that labor for American women is different today than it was in the 1950s, says Yasser El-Sayed, MD, obstetrician-in-chief at Lucile Packard Children’s Hospital. That’s because women themselves, along with advances in pain management, medical technology and monitoring during labor, have changed. Today, labor generally takes longer because the period of rapid cervical change, which Friedman called the “active” phase, starts later than it did for women in the 1950s.

An understanding of what makes labor normal is, of course, necessary for understanding what makes it abnormal. Obstetricians have traditionally used Friedman’s labor curve to help decide if it’s time to intervene, either with a caesarean section — the surgical delivery of the baby through the lower abdomen — or with operative vaginal delivery — using a grasping tool such as forceps to help. But C-sections, performed more often today than ever before, present their own risks, including predisposing women to disorders in future pregnancies. So, one major benefit of the new “normal” could be fewer C-sections, making childbirth safer for both mother and baby.

The new understanding is that, instead of a single definition of normal, there are several variations, all of which allow a woman to remain in the early (latent) phase of labor for two, three or even four hours longer than in decades past, before labor is considered abnormal. This is especially important for first-time mothers, who tend to labor longer than in subsequent pregnancies.

While the new research and labor curve catches up with the modern woman, there’s no question that Friedman’s study laid the groundwork for a common understanding of the progress of labor and the beginning of safe labor practices. In 1955, Friedman completed a real-time study of 500 Caucasian women giving birth, which he used to establish the progress of what would be for decades considered normal labor, segmenting it into stages, which were themselves broken into phases. He graphed the progress as a curve showing the opening, or dilation, of the cervix in relation to time. His curve, charted with time as the horizontal axis and dilation as the vertical, shows a line rising gradually until it reaches a cervical dilation of 4 centimeters, then steeply, as the cervix opens from 4 centimeters to 10 centimeters.

According to Friedman, a healthy, first-time mother should reach the active phase of the first stage of labor — when the cervix begins to open more rapidly and contractions increase and intensify — when her cervix has dilated 4 centimeters. Friedman expected the second stage of labor — beginning when her cervix is fully dilated (10 centimeters), and she starts to push the baby out — to take two hours. After two hours, if labor was not progressing — meaning the baby was not descending through the birth canal — Friedman advocated intervention with forceps or C-section.

Friedman gave doctors a standard for the outer limits of safety, which, over the years, became one of the primary justifications for medically necessary interventions. Other factors, like the baby’s heart rate, weight and position and the health of the mother, were also critical considerations.

Since then, the U.S. C-section rate has climbed, in part because the increasing safety of the surgery itself made it an appealing alternative when a difficult vaginal birth was anticipated. This expectation of safety and an uncomplicated delivery bred a threatening legal climate with severe and costly implications for doctors accused of not performing a timely C-section. This expectation also fostered an increasingly broad range of indications for C-section. Physician and patient preference may have played a role, although to a lesser degree: The ability to schedule the birth held a strong allure. Mothers who feared risks from vaginal birth — such as urinary incontinence — might choose an elective C-section. For doctors and pregnant women, C-section seemed a way to control risks, rather than a risk factor itself. All of these issues contributed to the U.S. C-section rate reaching an all-time high in 2009 at about 33 percent of all births, where it has held steady.

But with so many C-sections, their dangers have become easier to see. The mother’s recovery is harder, and she is more likely to face surgical risks such as infections and blood clots. Her chance of needing a C-section for later births rises dramatically. Worse, women who become pregnant following a C-section are at greater risk of placenta accreta, an abnormally deep attachment of the placenta to the wall of the uterus. [See story, page 18.] In many cases, a woman with placenta accreta must undergo hysterectomy — complete removal of her uterus — to avoid the risk of bleeding to death when the placenta is separated from her uterus.

“Placenta accreta has become a national epidemic,” says obstetrician-in-chief El-Sayed, who’s also a professor of obstetrics and gynecology at the Stanford University School of Medicine. “During my four-year residency in the early 1990s, I saw a handful of cases. We’re now treating two a month. And this is happening all over the country.”

New labor data

With their study of labor published in 1986, David Peisner, MD, and Mortimer Rosen, MD, of Cleveland Metropolitan General Hospital, concluded that labor generally progressed more slowly than Friedman had found. Their results, based on data from twice as many women as Friedman had studied, showed that only 50 percent of labors were active by 4 centimeters of cervical dilation. They wrote, “A patient who is not progressing in labor at 4 centimeters cervical dilation is not necessarily abnormal.”

Time would show that such patients were, in fact, the new normal. In 2010 the National Institute of Child Health and Human Development’s Consortium on Safe Labor, led by Jun Zhang, MD, PhD, looked back at the medical records of 62,415 first-time mothers to assess the labor patterns of women with a healthy, full-term delivery. They found the patterns at the turn of the millennium were very different from their mid-century cohorts. Most women in Zhang’s study weren’t transitioning to the active stage of labor until their cervix was dilated to 6 centimeters. What’s more, it was possible for at least two hours to pass in the active phase without much additional dilation.

What did this mean for the C-section rate? The consortium published a separate paper in 2010 based on 228,668 detailed labor and delivery records from 19 hospitals across the United States between 2002 and 2008. This study focused on the first delivery for each of the women, 30.5 percent of whom delivered by C-section. They found that 65 percent of C-sections performed due to “abnormal” labor were done in the first stage; 28 percent were done before dilation had reached 6 centimeters. With current studies now indicating that a normal active phase may not begin until 6 centimeters dilation, it’s clear that the majority of these labors may not have been abnormal at all and that many of these C-sections could have been avoided on the basis of timing alone.

The Consortium on Safe Labor’s landmark studies resulted in a new labor curve, also published in 2010, capturing the more diverse experiences of the modern woman in labor. Instead of a single line sloping up the graph to show full dilation over a set period of time, as Friedman’s curve did, the new curve shows four sets of staircases that step gradually up the chart. Each one has a unique starting point based on how dilated a woman’s cervix is when she is first admitted to the hospital in labor. Depending upon where she starts — 2, 3, 4 or 5 centimeters dilation — her progress toward 10 centimeters is measured differently, with a range of time allowed for each step.

Consortium researchers also looked at evidence as to why labor lasts longer today. For starters, moms today are slightly older and tend to weigh more than their Mad Men-era counterparts. That’s one finding from a 2012 study by Sarah Laughon, MD, of the National Institutes of Health, that compared the medical records of 39,491 women who gave birth between 1959 and 1966 with those of 98,359 women who gave birth between 2002 and 2008. And as Zhang’s study on C-sections showed, women who are overweight are more likely to have a C-section; as obesity rates in the United States have risen, so too have C-section rates.

“For both spontaneous and induced labors, C-sections were being done based on an understanding of labor that was informed by 1950s patients, as opposed to an understanding of labor that is steeped in data from a contemporary population,” says El-Sayed. “If we don’t understand what’s normal, then we end up doing interventions that may not need to happen.”

In February 2012, the National Institute for Child Health and Human Development, the Society for Maternal-Fetal Medicine and the American College of Obstetricians and Gynecologists gathered in Dallas for a workshop on reducing C-sections by preventing a woman’s first caesarean. They provided many recommendations for clinical practice, from which papers were distributed to obstetricians nationally. Many hospitals, like Packard Children’s, have adopted these new guidelines. The challenge for American hospitals and obstetricians now is to put these guidelines into routine practice everywhere.

“Changing practice takes a lot of time and involves a cultural change, but it will have a great impact. It’s wonderful news for mothers and babies,” El-Sayed says.

 

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