Objective
The objective of the study was to examine differences in labor patterns in a modern cohort compared with the 1960s in the United States.
Study Design
Data from pregnancies at term, in spontaneous labor, with cephalic, singleton fetuses were compared between the Collaborative Perinatal Project (CPP, n = 39,491 delivering 1959-1966) and the Consortium on Safe Labor (CSL; n = 98,359 delivering 2002-2008).
Results
Compared with the CPP, women in the CSL were older (26.8 ± 6.0 vs 24.1 ± 6.0 years), heavier (body mass index 29.9 ± 5.0 vs 26.3 ± 4.1 kg/m 2 ), had higher epidural (55% vs 4%) and oxytocin use (31% vs 12%), and cesarean delivery (12% vs 3%). First stage of labor in the CSL was longer by a median of 2.6 hours in nulliparas and 2.0 hours in multiparas, even after adjusting for maternal and pregnancy characteristics, suggesting that the prolonged labor is mostly due to changes in practice patterns.
Conclusion
Labor is longer in the modern obstetrical cohort. The benefit of extensive interventions needs further evaluation.
The original labor curve was created by Friedman in the 1950s. Zhang et al derived a labor curve from a much larger cohort of women from the 1960s using data from the National Collaborative Perinatal Project (CPP). Differences between these 2 labor curves are apparent, most notably that the nulliparous women in the CPP demonstrated a more gradual transition to active phase, that active phase labor in the multiparous women began around 5 cm cervical dilation, and that women in the CPP lacked the deceleration phase described by Friedman.
More recently the Consortium on Safe Labor (CSL) assessed labor progression in a large, contemporary cohort of women who presented in spontaneous labor. The CSL analysis found that the rate of cervical dilation was slower in all parities compared with that described by Friedman, especially from 4 to 6 cm, with an acceleration point suggesting active phase that occurred much later (around 6 cm).
However, since the 1960s, both maternal characteristics and obstetric practices have changed considerably. Women are older and have higher body mass indices (BMI), oxytocin and epidural use are more common, and more women undergo induction of labor in current practice. Both increasing maternal age and BMI are associated with progressively longer labor. Epidurals and induction have also been shown to be associated with longer labor. Because maternal characteristics are less modifiable, it is important to know the effects of current obstetric practice on the changes in labor patterns. Thus, we used data from the contemporary CSL study and data from the CPP to examine the differences in labor patterns and outcomes in modern obstetrics compared with the 1960s in women with spontaneous labor. We hypothesized that longer labor in the modern cohort was due to both changes in obstetric practices as well as changes in maternal characteristics.
Materials and Methods
The course of labor and method of delivery were compared between the CPP and the CSL. The CPP was a prospective study of 54,390 births to 48,197 women recruited from 1959 to 1965 (last delivery in 1966). Women were enrolled at 12 university clinical centers across the United States, and detailed information on demographics, medical history, socioeconomic status, and behavior were collected via interviews. A physical examination and blood sample were also performed at the first visit. The women were followed up throughout pregnancy, and repeat interviews and physical examinations were performed. Upon admission to labor and delivery, a trained observer recorded the cervical examinations as well as all labor and delivery, postpartum, and neonatal events. A senior obstetrician also completed a summary of the pregnancy and labor and delivery. Children were followed up to age 7 years.
The CSL was a retrospective cohort study conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, and included women giving birth between 2002 and 2008, with the majority (87%) between 2005 and 2007. There were 228,668 deliveries from 12 clinical centers and 19 hospitals representing 9 American College of Obstetrics and Gynecology districts. Institutional review board approval was obtained by all participating institutions.
Data were extracted from the patient electronic medical records including demographic data, medical history, and labor and delivery information as well as obstetrical, postpartum, and neonatal outcomes. Data from the neonatal intensive care unit were collected and linked to the newborn record. Maternal and newborn discharge International Classification of Diseases , ninth revision, codes were also collected for each delivery. Data were transferred in electronic format from each site and were mapped to common categories for each predefined variable at the data coordinating center. Investigators at each site completed surveys on hospital and physician characteristics. Data inquiries, cleaning, and logic checking were performed. Validation studies were performed for 4 key variables and the electronic medical records were found to be an accurate representation of the medical charts.
There were 54,304 observations in the CPP obstetrical data file, and we limited our analysis to each individual woman’s first enrolled pregnancy (n = 44,669) to avoid an intraperson correlation. Only women who presented in spontaneous labor were included, leaving 39,491 for analysis. In the CSL database, there were 228,668 deliveries, and we included 208,695 observations from each individual woman’s first enrolled pregnancy. Only women who presented in spontaneous labor and had a singleton gestation were included, for a total of 98,359 women. There were a total of 137,850 women in the combined CPP plus CSL dataset.
Statistical Methods
The maternal, labor, and neonatal characteristics of women by study were compared using χ 2 and the Wilcoxon rank-sum test where applicable ( Table 1 ). To compare continuous demographic or neonatal characteristics and calculate the P values ( Tables 2-4 ), we used a linear regression with a term for study (CPP or CSL). For binary variables, we used linear probability models (PROC GENMOD with binomial distribution and identity link in SAS; SAS Institute, Cary, NC) to obtain the adjusted mean differences and associated P values. When linear probability models failed to converge, we used instead a logistic regression to produce the corresponding P values. Labor progression transition times from 1 cm to another were estimated by fitting an interval censored regression (using PROC LIFEREG of SAS), as previously described by Zhang et al.
| Demographic information | CPP (n = 39,491) | CSL (n = 98,359) |
|---|---|---|
| Maternal age, y (mean ± SD) | 24.1 ± 6.0 | 26.8 ± 6.0 |
| Prepregnancy BMI, kg/m 2 | 22.6 ± 4.2 | 24.6 ± 5.6 |
| Delivery BMI, kg/m 2 | 26.3 ± 4.1 | 29.9 ± 5.0 |
| Maternal race, % | ||
| White | 43 | 50 |
| Black | 48 | 21 |
| Hispanic | 9 | 18 |
| Other | 0 | 11 |
| Gestational age at delivery (mean ± SD, wks) | 39.2 ± 3.4 | 38.5 ± 2.3 |
| Parity | ||
| 0 | 38 | 44 |
| 1 | 21 | 28 |
| ≥2 | 41 | 28 |
| Spontaneous ROM prior to admission, % | 14 | 39 |
| Labor characteristics | ||
| Epidural, % | 4 | 55 |
| Oxytocin augmentation, % | 12 | 31 |
| Forceps, % | 40 | 2 |
| Vacuum, % | 0.1 | 4 |
| Forceps or vacuum, % | 40 | 6 |
| Episiotomy, % | 68 | 18 |
| Third- or fourth-degree laceration | 4 | 2 |
| Intrapartum cesarean delivery, % | 3 | 12 |
| Neonatal characteristics | ||
| Birthweight, g (mean ± SD) | 3133 ± 596 | 3232 ± 570 |
| Ethnicity | ||
| White | 3257 ± 584 | 3297 ± 515 |
| Black | 3022 ± 592 | 3085 ± 618 |
| Hispanic | 3129 ± 557 | 3240 ± 572 |
| Other | — | 3215 ± 542 |
| Parameter | CPP (n = 14,791) | CSL (n = 43,576) | Adjusted median difference a | Adjusted P value |
|---|---|---|---|---|
| Maternal age, y (mean ± SD) | 20.4 ± 4.0 | 24.4 ± 5.7 | < .001 | |
| Delivery BMI, kg/m 2 | 25.5 ± 3.4 | 29.6 ± 4.9 | < .001 | |
| Admission characteristics | ||||
| Gestational age at delivery, wks | 39.3 ± 3.4 | 38.6 ± 2.4 | < .001 | |
| Dilation on admission | ||||
| Median (10th, 90th percentiles) | 3 (1, 6.5) | 3.5 (1, 7) | ||
| Mean ± SD | 3.5 ± 2.2 | 3.8 ± 2.3 | 0.6 b | < .001 |
| Effacement on admission | ||||
| Median (10th, 90th percentiles) | 85 (40, 100) | 90 (60, 100) | ||
| Mean ± SD | 77 ± 25 | 84 ± 18 | 7.3 b | < .001 |
| Spontaneous ROM prior to admission, % | 16 | 41 | 18 | < .001 |
| Labor characteristics | ||||
| Epidural, % | 5 | 60 | 37 | < .001 |
| Oxytocin augmentation, % | 16 | 37 | 8 | < .001 |
| First-stage durations, h (median, 95th percentiles) | ||||
| From 4 cm to C/C | 3.9 (18.5) | 6.5 (24.0) | 2.6 | < .001 |
| From 5 cm to C/C | 2.1 (11.8) | 3.6 (15.1) | 1.3 | < .001 |
| From 6 cm to C/C | 1.2 (8.2) | 2.2 (10.0) | 0.7 | < .001 |
| Second-stage durations, h | ||||
| With spontaneous delivery (median, 95th percentiles) | 0.45 (2.0) | 0.90 (3.1) | 0.22 | < .001 |
| With assisted delivery (median, 95th percentiles) | 0.75 (3.1) | 1.65 (4.25) | 0.49 | < .001 |
| Forceps, % | 66 | 3 | –51 | < .001 |
| Vacuum, % | 0.2 | 6 | 4 | < .001 |
| Forceps or vacuum, % | 66 | 10 | –47 | < .001 |
| Episiotomy, % | 92 | 27 | –51 | < .001 |
| Third- or fourth-degree laceration, % | 8 | 5 | –4 | < .001 |
| Intrapartum cesarean delivery, % | 3 | 16 | 5 | < .001 |
| Neonatal characteristics | ||||
| Birthweight, g (mean ± SD) | 3077 ± 571 | 3190 ± 573 | ||
| Apgar score at 1 min (mean) | 7.5 ± 2.1 | 7.9 ± 1.4 | ||
| <4, % | 7 | 3 | ||
| 4-6 | 17 | 6 | ||
| ≥7 | 76 | 91 | ||
| Apgar score at 1 min <7, % | 24 | 9 | –13 | < .001 |
| Apgar score at 5 min (mean) | 8.9 ± 1.4 | 8.8 ± 0.8 | ||
| <4, % | 1.8 | 0.5 | ||
| 4-6 | 3.9 | 1.3 | ||
| ≥7 | 94.4 | 98.2 | ||
| Apgar score at 5 min <7, % | 6 | 2 | –4 | < .001 |
a Median difference (except where noted) for parameter in the CSL minus the CPP, adjusted for maternal age, race, gestational age at delivery, BMI at delivery, spontaneous rupture of membranes, and birthweight;
| Parameter | CPP (n = 8337 ) | CSL (n = 27,471) | Adjusted median difference a | Adjusted P value |
|---|---|---|---|---|
| Maternal age, y (mean ± SD) | 23.1 ± 4.6 | 27.3 ± 5.6 | < .001 | |
| Delivery BMI, kg/m 2 | 26.0 ± 3.9 | 29.9 ± 4.9 | < .001 | |
| Admission characteristics | ||||
| Gestational age at delivery, wks | 39.3 ± 3.3 | 38.5 ± 2.2 | < .001 | |
| Dilation on admission | ||||
| Median (10th, 90th percentiles) | 4 (2, 8) | 4 (2, 8) | ||
| Mean ± SD | 4.3 ± 2.4 | 4.6 ± 2.3 | 0.6 b | < .001 |
| Effacement on admission | ||||
| Median (10th, 90th percentiles) | 80 (40, 100) | 90 (50, 100) | ||
| Mean ± SD | 75 ± 25 | 82 ± 20 | 7 b | < .001 |
| Spontaneous ROM prior to admission, % | 13 | 36 | 19 | < .001 |
| Labor characteristics | ||||
| Epidural, % | 3 | 52 | 34 | < .001 |
| Oxytocin augmentation, % | 10 | 25 | 6 | < .001 |
| First-stage durations, h (median, 95th percentiles) | ||||
| From 5 cm to C/C | 1.2 (7.9) | 3.0 (15.0) | 2.0 | < .001 |
| From 6 cm to C/C | 0.6 (4.8) | 1.6 (8.9) | 0.9 | < .001 |
| Second-stage durations, h | ||||
| With spontaneous delivery (median, 95th percentiles) | 0.18 (0.72) | 0.33 (1.67) | 0.10 | < .001 |
| With assisted delivery (median, 95th percentiles) | 0.38 (1.28) | 0.62 (3.08) | 0.26 | < .001 |
| Forceps, % | 36 | 0.8 | –29 | < .001 |
| Vacuum, % | 0.1 | 2 | 2 | .003 |
| Forceps or vacuum, % | 36 | 4 | –27 | < .001 |
| Episiotomy, % | 76 | 13 | –52 | < .001 |
| Third- or fourth-degree laceration, % | 3 | 1 | –2 | .001 |
| Intrapartum cesarean delivery, % | 2 | 10 | 3 | < .001 |
| Neonatal characteristics | ||||
| Birthweight, g (mean ± SD) | 3147 ± 571 | 3264 ± 553 | ||
| Apgar score at 1 min (mean) | 7.9 ± 1.9 | 8.1 ± 1.3 | ||
| <4, % | 4.6 | 2.1 | ||
| 4-6 | 12.6 | 4.2 | ||
| ≥7 | 82.8 | 93.8 | ||
| Apgar score at 1 min <7, % | 17 | 6 | –11 | < .001 |
| Apgar score at 5 min (mean) | 9.1 ± 1.1 | 8.9 ± 0.7 | ||
| <4, % | 1.0 | 0.4 | ||
| 4-6 | 2.6 | 0.8 | ||
| ≥7 | 96.4 | 98.8 | ||
| Apgar score at 5 min <7, % | 4 | 1 | –3 | < .001 |
a Median difference (except where noted) for parameter in the CSL minus the CPP, adjusted for maternal age, race, gestational age at delivery, BMI at delivery, spontaneous rupture of membranes, and birthweight;
| Parameter | CPP (n = 16,277) | CSL (n = 27,312) | Adjusted median difference a | Adjusted P value |
|---|---|---|---|---|
| Maternal age, y (mean ± SD) | 28.0 ± 5.7 | 30.1 ± 5.3 | < .001 | |
| Delivery BMI, kg/m 2 | 27.1 ± 4.5 | 30.4 ± 5.1 | < .001 | |
| Admission characteristics | ||||
| Gestational age at delivery, wks | 39.1 ± 3.5 | 38.4 ± 2.2 | < .001 | |
| Dilation on admission | ||||
| Median (10th, 90th percentiles) | 4 (1.5, 8) | 4 (2, 8) | ||
| Mean ± SD | 4.2 ± 2.4 | 4.7 ± 2.4 | 0.8 b | < .001 |
| Effacement on admission | ||||
| Median (10th, 90th percentiles) | 75 (25, 100) | 80 (50, 100) | ||
| Mean ± SD | 68 ± 28 | 80 ± 20 | 12 b | < .001 |
| Spontaneous ROM prior to admission, % | 13 | 38 | 19 | < .001 |
| Labor characteristics | ||||
| Epidural, % | 4 | 48 | 30 | < .001 |
| Oxytocin augmentation, % | 9 | 27 | 9 | < .001 |
| First-stage durations, h (median, 95th) | ||||
| From 5 cm to C/C | 1.0 (8.6) | 2.8 (15.5) | 2.0 | < .001 |
| From 6 cm to C/C | 0.5 (5.1) | 1.3 (8.9) | 0.9 | < .001 |
| Second-stage durations, h | ||||
| With spontaneous delivery (median, 95th percentiles) | 0.15 (0.60) | 0.20 (1.0) | 0.05 | < .001 |
| With assisted delivery (median, 95th percentiles) | 0.35 (1.18) | 0.42 (2.11) | 0.12 | < .001 |
| Forceps, % | 18 | 0.5 | –15 | < .001 |
| Vacuum, % | 0.1 | 1.7 | 2 | < .001 |
| Forceps or vacuum, % | 18 | 2.5 | –14 | < .001 |
| Episiotomy, % | 36 | 7 | –25 | < .001 |
| Third- or fourth-degree laceration, % | 1 | 0.3 | –1 | .1 |
| Intrapartum cesarean delivery, % | 2 | 7 | 3 | < .001 |
| Neonatal characteristics | ||||
| Birthweight, g (mean ± SD) | 3176 ± 625 | 3269 ± 577 | ||
| Apgar score at 1 min (mean) | 8.0 ± 1.9 | 8.2 ± 1.3 | ||
| <4, % | 5 | 2 | ||
| 4-6 | 12 | 4 | ||
| ≥7 | 83 | 94 | ||
| Apgar score at 1 min <7, % | 17 | 6 | –11 | < .001 |
| Apgar score at 5 min (mean) | 9.0 ± 1.3 | 8.9 ± 0.8 | ||
| <4, % | 1.5 | 0.6 | ||
| 4-6 | 2.8 | 0.8 | ||
| ≥7 | 95.7 | 98.6 | ||
| Apgar score at 5 min <7, % | 4 | 1 | –3 | < .001 |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
