NEW YORK (Reuters Health) Dec 24 – Women today experience progression of labor later in the dilation process than women decades ago, and obstetrical practice must be changed in order to reflect this shift, the authors of a new study involving than 60,000 contemporary women concludes.
Allowing women more time to progress to 6 centimeters could likely reduce the rate of both intrapartum and repeat cesarean sections in the US, say researchers led by Dr. Jun Zhang of the National Institute of Child Health and Human Development in Bethesda, Maryland.
Right now, Dr. Zhang and colleagues note in the December issue of Obstetrics & Gynecology, obstetricians use labor curves developed in the 1950s by Dr. Emanuel Friedman to determine whether a woman’s labor is progressing normally. But given that women are having children later, maternal and fetal body sizes are increasing, and obstetric interventions are being used more often, these guidelines may no longer apply, they add.
To investigate, the researchers gathered data from 19 US hospitals on 62,415 parturients. All of the women had singleton babies with vertex presentation delivered vaginally at term, spontaneous onset of labor, and normal perinatal outcomes. The researchers used electronic medical records from 2002-2008, with nearly 90% of the births taking place in 2005-2007.
Nearly half of the women were given oxytocin to aid in labor progression, while 80% had epidural analgesia.
Upon admission, the median cervical dilation for nulliparous women was 4 centimeters, compared to 4.5 centimeters for women who had already had one child and 5 centimeters for women who had given birth two or more times previously. The median effacement was, respectively, 90%, 90%, and 80%.
On average, the labor curves for nulliparous women showed no inflection point at which progression began to accelerate. Multiparous women labored at the same rate as nulliparous women up to 6 centimeters’ dilation, but showed “much faster” acceleration afterwards.
When the researchers looked at labor duration from one centimeter of dilation to the next, they found women could take more than six hours to progress from 4 centimeters to 5 centimeters, while progression from 5 to 6 centimeters could take more than three hours.
The 95th percentile duration for the second stage of labor was 3.6 hours in nulliparous women who had epidural analgesia, and 2.8 hours in first-time mothers who didn’t have epidurals.
Based on the findings, the researchers developed a partogram for use with nulliparous women to determine when labor should be considered protracted. “Our study with a contemporary population observed several important differences from the classical Friedman curve,” the researchers write. “It became clear that there are a substantial number of parturients who may not have a consistent pattern for the active phase of labor, particularly in nulliparous women.” These women may have more gradual progression of labor, Dr. Zhang and colleagues explain, but still deliver vaginally.
Also, the researchers state, the new data suggest that the active phase of labor often doesn’t start until 6 centimeters dilation or later, compared to the “commonly used milestone” of 4 centimeters.
“Judging whether a woman is having labor protraction and arrest should not be based on a research definition of an average starting point or average duration of labor,” the researchers write. Instead, an upper limit of what is considered ‘normal labor’ should be used in patient management. “As long as the labor is within a normal range and other maternal and fetal conditions are reassuring, a woman should be allowed to continue the labor process.”
The differences they observed could be due to the fact that women giving birth are older and heavier, on average, than they were when Dr. Friedman’s labor curves were developed, the researchers note; “these factors are known to affect labor progress and duration.”
SOURCE: http://link.reuters.com/ruk42r
Obstet Gynecol 2010;116:1281-1287.
