Transactions of The Twenty-Second Annual Meeting of The Society for Maternal-Fetal Medicine
Reassessing the labor curve in nulliparous women

Presented at the Twenty-second Annual Meeting of the Society for Maternal-Fetal Medicine, New Orleans, La, January 14-19, 2002.
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Abstract

Objectives: Our purpose was to examine the pattern of labor progression in nulliparous parturients in contemporary obstetric practice. Study Design: We extracted detailed labor data from 1329 nulliparous parturients with a term, singleton, vertex fetus of normal birth weight after spontaneous onset of labor. Cesarean deliveries were excluded. We used a repeated-measures regression with a 10th-order polynomial function to discover the average labor curve under contemporary practice. With use of an interval-censored regression with a log normal distribution, we also computed the expected time interval of the cervix to reach the next centimeter, the expected rate of cervical dilation at each phase of labor, and the duration of labor for fetal descent at various stations. Results: Our average labor curve differs markedly from the Friedman curve. The cervix dilated substantially slower in the active phase. It took approximately 5.5 hours from 4 cm to 10 cm, compared with 2.5 hours under the Friedman curve. We observed no deceleration phase. Before 7 cm, no perceivable change in cervical dilation for more than 2 hour was not uncommon. The 5th percentiles of rate of cervical dilation were all below 1 cm per hour. The 95th percentile of time interval for fetal descent from station +1/3 to +2/3 was 3 hours at the second stage. Conclusion: Our results suggest that the pattern of labor progression in contemporary practice differs significantly from the Friedman curve. The diagnostic criteria for protraction and arrest disorders of labor may be too stringent in nulliparous women. (Am J Obstet Gynecol 2002;187:824-8.)

Section snippets

Material and methods

We used data from a previous study in which detailed labor and delivery information was collected.8 In brief, we systematically selected 1329 subjects from 1992 to 1996 on the basis of the following inclusion criteria: nulliparous, singleton pregnancy, maternal age between 18 and 34 years, gestational age between 37 weeks 0 days and 41 weeks 6 days, birth weight between 2500 and 4000 g, spontaneous onset of labor, vertex presentation at admission, cervical dilation <7 cm at admission, and

Results

Our study population consisted of women with a mixed race/ethnicity: 65% non-Hispanic white, 12% non-Hispanic black, 7% Hispanic, 11% Asian, and 5% other. Mean maternal age was 23 years; mean maternal height and weight at delivery were 64 inches and 169 pounds, respectively; mean gestational age was 39.3 weeks. At admission, the median cervical dilation was 3.5 cm (10th and 90th percentiles: 1.5 and 5.0 cm, respectively). Thirty-eight percent had complete effacement and 35% had ruptured

Comment

Our study indicates that the pattern of labor progression in contemporary practice is markedly different from what was observed in the 1950s. Labor appears to progress more slowly now than the Friedman curve indicates. This finding is consistent with previous studies. For example, Friedman2 showed that his study population who were delivered in the 1950s had a mean duration of active phase of 4.6 hours, which was similar to the observation by Hendricks et al11 in the 1960s. However, data from

Acknowledgements

We thank Dr Watson A. Bowes, Jr, for his valuable comments on the manuscript.

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Reprint requests: Jun Zhang, PhD, MD, Epidemiology Branch, National Institute of Child Health and Human Development, National Institutes of Health, Building 6100, Room 7B03, Bethesda, MD 20892. E-mail: [email protected]

b

†Deceased.

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