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National trends in primary cesarean delivery, labor attempts, and labor success, 1990-2010

Published:August 16, 2013DOI:https://doi.org/10.1016/j.ajog.2013.08.012

      Objective

      The national primary cesarean delivery rate increased until 2004, but after 2004, this rate cannot be tracked using Vital Statistics data. Additionally, it is unknown whether changes in the primary cesarean delivery rate reflect changes in the rate of labor attempts, labor success, or both. Here, using hospital discharge data, we examined national trends in primary cesarean deliveries, labor attempts, and labor success among women without prior cesarean delivery between 1990 and 2010.

      Study Design

      This analysis of serial cross-sectional data from the National Hospital Discharge Survey used Joinpoint regression to assess trends over time and logistic regression with marginal effects to identify rates of change over time and adjust for demographic and clinical factors.

      Results

      The primary cesarean delivery rate declined 0.2 percentage points per year (95% confidence interval [CI], 0.1–0.3) between 1990 and 1999, increased 1.0 percentage point per year (95% CI, 0.8–1.2) between 1999 and 2004, and increased 0.3 percentage points (95% CI, 0.1–0.6) per year from 2004 until 2010. Between 1998 and 2005, the rate of labor attempts declined 0.4 percentage points (95% CI, 0.3–0.5) per year. No changes in the labor attempt rate occurred between 2005 and 2010. Labor success rates increased 0.2 percentage points (95% CI, 0.1–0.3) per year between 1990 and 1998 but then declined 0.5 (95% CI, 0.5–0.8) percentage points per year from 1998 to 2010. Adjusted results were similar.

      Conclusion

      The primary cesarean delivery rate continued to increase after 2004. Increases in the primary cesarean delivery rate after 2005 were driven by declines in labor success rates.

      Key words

      The rate of cesarean deliveries increased from 22.7% of all births in 1990 to 32.8% of all births in 2010.
      • Martin J.
      • Hamilton B.
      • Ventura S.
      • Osterman M.
      • Wilson E.
      • Mathews T.
      Births: final data for 2010.
      Many studies have explored reasons for changes in vaginal birth after cesarean rates.
      National Institutes of Health Consensus Development Conference Panel
      National Institutes of Health Consensus Development conference statement: vaginal birth after cesarean: new insights March 8-10, 2010.

      Oregon Health and Science University. Evidence-based Practice Center, United States. Agency for Healthcare Research and Quality. Vaginal birth after cesarean: new insights. Rockville, MD: Agency for Healthcare Research and Quality, US Department of Health and Human Services.

      However, primary cesarean deliveries likely make up more than half of all cesarean deliveries in the United States.
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • Ventura S.J.
      • Menacker F.
      • Kirmeyer S.
      Births: final data for 2004. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      • MacDorman M.
      • Declercq E.
      • Menacker F.
      Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.
      • Menacker F.
      • Curtin S.C.
      Trends in cesarean birth and vaginal birth after previous cesarean, 1991-99. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      • Joesch J.M.
      • Gossman G.L.
      • Tanfer K.
      Primary cesarean deliveries prior to labor in the United States, 1979-2004.
      The national primary cesarean delivery rate increased from 14.6% of births in 1996 to 20.6% in 2004, accounting for approximately 60% of the increase in total cesarean deliveries.
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • Ventura S.J.
      • Menacker F.
      • Kirmeyer S.
      Births: final data for 2004. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      This increase is concerning because cesarean delivery is associated with short-term complications such as intraoperative injury to the bowel, bladder or ureter, hemorrhage, infection, and thromboembolism.

      Cunningham FG, Williams JW. Williams obstetrics. New York: McGraw-Hill, Medical.

      It also has longer-term consequences in subsequent pregnancies such as placenta accreta, uterine rupture, intraoperative injury of the uterus, bowel, ureter, or bladder from adhesions and an increased risk of hysterectomy.
      • Clark E.A.
      • Silver R.M.
      Long-term maternal morbidity associated with repeat cesarean delivery.
      To address this increase in cesarean delivery, a recent national workgroup has examined indications for cesarean with the aim of reducing primary cesarean deliveries.
      • Spong C.Y.
      • Berghella V.
      • Wenstrom K.D.
      • Mercer B.M.
      • Saade G.R.
      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.
      After 2004, because of changes in the collection of birth certificate data, primary cesarean delivery rates cannot be calculated for all states from the National Vital Statistics System and instead must be based on vital statistics from a subnational group of states.
      • MacDorman M.
      • Declercq E.
      • Menacker F.
      Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.
      Because of this limitation, national trends in primary cesarean deliveries since 2004 are unknown. Previous studies have examined single hospital trends
      • Barber E.L.
      • Lundsberg L.S.
      • Belanger K.
      • Pettker C.M.
      • Funai E.F.
      • Illuzzi J.L.
      Indications contributing to the increasing cesarean delivery rate.
      or hospital consortium data to estimate primary cesarean rates at a single point in time,
      • Zhang J.
      • Troendle J.
      • Reddy U.M.
      • et al.
      Contemporary cesarean delivery practice in the United States.
      but to our knowledge, no studies have examined national trends over time since 2004. Analysis of hospital discharge data provides a means of estimating national primary cesarean delivery rates since 2004, but this has not been done previously.
      The rate of primary cesarean deliveries depends on the rate at which labor is attempted and the rate at which labor successfully leads to vaginal births in women without previous cesarean deliveries. Decreases in rates of both labor attempts and labor success contributed significantly to recent increases in repeat cesarean deliveries.
      • Uddin S.F.
      • Simon A.E.
      Rates and success rates of trial of labor after cesarean delivery in the United States, 1990-2009.
      However, previous studies have not examined how each of these factors might contribute to trends in the national primary cesarean delivery rate.
      The aim of this study was to examine trends in the national rate of primary cesarean delivery, especially after 2004, and examine the impact of changes in the attempted labor and labor success rates on these trends.

      Materials and Methods

      This analysis of serial cross-sectional data used data from the National Hospital Discharge Survey (NHDS) from 1990 to 2010 to examine changes over time in the rates of primary cesarean delivery, attempted labor, and labor success. NHDS is an annual cross-sectional, nationally representative sample survey of hospital discharges from nonfederal, noninstitutional short-stay US hospitals, conducted by the National Center for Health Statistics (NCHS) from 1965 to 2010. The sampling strata of the NHDS include hospital size and geography (census region and metropolitan and nonmetropolitan statistical areas) to ensure broad geographic and hospital size representation in the data. For 1990 through 2007, NHDS collected data on an average of 309,000 hospital discharges per year from an average of 459 hospitals. Due to NCHS funding limitations, the sample of hospitals was reduced by half for 2008-2010, and data were collected from only 160,000 discharges from 205 hospitals.
      National Center for Health Statistics
      National Hospital Discharge Survey—2008. Public Use Data File Documentation.
      NHDS has a 3-stage sampling design, and sample weights were calculated based on the reciprocal of selection probability and adjusted for nonresponse. Details of survey methodology and weighting procedures have been previously described.
      • Dennison C.F.
      • Pokras R.
      Design and operation of the National Hospital Discharge Survey 1988 Redesign.
      NHDS has received approval by the NCHS Research Ethics Review Board. This study used NHDS data and did not require separate institutional review board approval.
      Data from the Vital Statistics system could not be used for this analysis because, prior to the 2003 revision of the birth certificate, information on whether a woman underwent labor was not collected on the birth certificate. By 2010, only 33 states had adopted the 2003 revision of the birth certificate; these states are not considered a random sample or representative of the United States, making a calculation of trends in national estimates after 2004 impossible.
      Cases were defined as discharges with International Classification of Diseases-9th Revision Clinical Modification (ICD-9-CM) codes indicating delivery. Determination of whether the patient underwent labor during the current delivery, had a vaginal or cesarean delivery, and whether the patient had a previous cesarean delivery or the other clinical conditions listed in Table 1 was made by the presence of the relevant ICD-9-CM codes (Table 1). Deliveries with labor were identified using a modified list of codes used in previous studies (Table 1).
      • Gregory K.D.
      • Korst L.M.
      • Gornbein J.A.
      • Platt L.D.
      Using administrative data to identify indications for elective primary cesarean delivery.
      • Henry O.A.
      • Gregory K.D.
      • Hobel C.J.
      • Platt L.D.
      Using ICD-9 codes to identify indications for primary and repeat cesarean sections: agreement with clinical records.
      The ICD-9-CM codes used in the calculation of primary cesarean delivery, attempted labor, and labor success have been validated against clinical data in previous research.
      • Henry O.A.
      • Gregory K.D.
      • Hobel C.J.
      • Platt L.D.
      Using ICD-9 codes to identify indications for primary and repeat cesarean sections: agreement with clinical records.
      Table 1ICD-9-CM codes used for case identification
      CategoryICD-9-CM Codes
      Delivered
       Diagnosis codeV27
       Procedure codes72, 74.0-74.2, 74.4, 74.9
      Previous cesarean delivery
       Diagnosis code654.2
      Cesarean delivery
       Procedure codes74.0-74.2, 74.4, 74.9
      Labored
       Diagnosis codes650, 653.4-653.5, 653.8-653.9, 658.2, 658.3, 659.0-659.3, 660-662, 664, 665.1
       Procedure codes72.0-72.4, 73.01, 73.09, 73.1, 73.3-73.6, 73.93-73.99, 75.32, 75.38, 75.6
      Hypertension
       Diagnosis codes642.0-642.9
      Diabetes
       Diagnosis codes648.0, 648.8, 250
      Placenta previa
       Diagnosis codes641.0-641.1
      Preterm delivery
       Diagnosis codes644.2
      Multiple gestation
       Diagnosis codesV27.2-V27.7, 651
      Genital herpes
       Diagnosis codes054.1
      Breech presentation
       Diagnosis codes652.1-652.2
      ICD-9-CM, International Classification of Diseases-9th Revision Clinical Modification.
      Simon. Trends in primary cesarean and labor. Am J Obstet Gynecol 2013.
      Our study population included only those cases without a diagnosis code for previous cesarean delivery. The primary cesarean delivery rate was calculated for each year as the percent of discharges with a cesarean delivery divided by the total number of discharges with deliveries in our study population. The attempted labor rate in our study sample was calculated for each year as the number of discharges with no previous cesarean deliveries that also had ICD-9-CM codes for labor divided by the total number of discharges with deliveries and no previous cesarean delivery. Delivered cases with labor but with no procedure codes for cesarean delivery were considered to have had successful labor resulting in a vaginal birth. For each year, the rate of successful labor among women without a previous cesarean delivery was calculated as the number of vaginal births divided by the number of women who labored. Rates and associated SEs were estimated for each year from 1990 through 2010 using Stata 12.0 SE (StataCorp, College Station, TX) and adjusted for the complex design of the survey using Taylor series linear approximation.
      Estimates of yearly primary cesarean rates and associated SEs were entered into a Joinpoint regression using the National Cancer Institute's Joinpoint 3.4.3 software

      National Cancer Institute. Joinpoint software; 2011.

      using year as the independent variable and primary cesarean rate as the dependent variable. Joinpoint was used to identify time points (joinpoints) in which linear trends changed. Joinpoint regression fits the simplest linear model with no changes in trend (a straight line) and, using a series of Monte Carlo permutation tests, tests whether 1 or more joinpoints (changes in linear trend) are statistically significant and should be added to the model. Similarly, the rates of attempted labor and labor success among women without previous cesarean delivery and associated SEs were entered into 2 additional Joinpoint regressions as dependent variables with year as the independent variable for each.
      The trends identified in Joinpoint were further investigated using logistic regression in Stata 12.0 SE. We conducted 3 sets of logistic regressions. The first set used primary cesarean delivery as the dependent variable, the second set used attempted labor as the dependent variable, and the third set used labor success as the dependent variable. For each dependent variable, regressions were conducted for each time period identified as a separate trend by Joinpoint regression. For each time period identified by Joinpoint, 2 models were conducted: an unadjusted model with only year as the independent variable and an adjusted model.
      All adjusted models included maternal age (greater than or less than 35 years), hospital bed size (less than 50, 50-99, 100-199, 200-299, 300-499, 500-999, or 1000 or more beds), US Census region (Northeast, Midwest, South, and West), and expected source of payment (private insurance, Medicare, Medicaid, uninsured, other/unknown). Adjusted models using labor success as the dependent variable also included factors that may affect labor success (preterm delivery, multiple gestation, hypertension, diabetes, large for gestational age, intrauterine growth restriction, and fetal anomalies) as independent variables. Adjusted models using attempted labor as the dependent variable and adjusted models using primary cesarean delivery as the dependent variable included clinical factors that may influence the decision to attempt labor (all variables included in the models for labor success in addition to placenta previa, genital herpes, and breech presentation). For each regression, marginal effects were calculated for the survey year variable.
      Additionally, these analyses were repeated with only singleton, term deliveries to assess unadjusted and adjusted trends over time in a more homogeneous population of births. Finally, these analyses were also repeated including additional ICD-9-CM codes that might, but did not necessarily, indicate labor (fetal distress, 656.3, and fetal heart rate abnormalities, 659.7).
      No observations had missing data for hospital bed size or US Census region. Age was missing for 0.1% of observations. Values imputed for these observations by NCHS on the NHDS file were used. Expected source of payment had a value of unknown or other for 1.9% of observations. These were included in regressions as a separate category because this category may be informative, rather than represent only missing data.
      From 1990 to 2007, there were 338-400 hospitals that contributed discharges with deliveries in the NHDS. From 2008 to 2010, there were 158-162 hospitals that contributed discharges with deliveries, as NCHS reduced the size of the survey.
      National Center for Health Statistics
      National Hospital Discharge Survey—2008. Public Use Data File Documentation.
      The estimated number of total deliveries for each year ranged from 3,738,000 in 2000 to 4,144,000 in 2008.
      The NHDS reports rates per 100 deliveries, with multiple gestation births counted as a single delivery, whereas vital statistics reports rates per 100 births. Also, data from NHDS include only births that occur within hospitals, whereas Vital Statistics include out-of-hospital births. After accounting for these factors, the confidence interval of the NHDS estimate for deliveries in each year always included the number of births obtained from the Vital Statistics system (data not shown). Although regression analyses were conducted using unrounded estimates, the weighted estimates presented were rounded to the nearest 1000 cases to be consistent with NCHS practice. NCHS recommends rounding NHDS estimates to the nearest thousand to imply an appropriate level of precision for this survey.
      • Pokras R.
      Trends in hospital utilization: United States, 1965-86. Vital and Health Statistics Series 13.
      All estimates met criteria of statistical reliability of a relative standard error of less than 30% and a sample size of greater than 30 observations.
      National Center for Health Statistics
      National Hospital Discharge Survey—2008. Public Use Data File Documentation.
      Results within each analysis were considered significant at values of P < .05.

      Results

      Annual estimates from 1990 to 2010 for the number of deliveries by women without previous cesarean ranged from a high of 3,601,000 in 1990 to a low of 3,290,000 in 2000 (Table 2). The number of primary cesarean deliveries between 1990 and 2010 ranged from 519,000 in 1995 to 781,000 in 2007 (Table 2). The primary cesarean delivery rate reached low levels of 15.5% in both 1995 (95% confidence interval [CI], 14.7–16.3%) and 1999 (95% CI, 14.9–16.1%) and a high of 23.1% (95% CI, 21.7–24.5%) in 2010 (Figure 1). Joinpoint regression identified 2 significant joinpoints, 1999 and 2004. The unadjusted trend between 1990 and 1999 showed a decline of 0.2 percentage point per year (P < .01) (Table 3). The unadjusted trend between 1999 and 2004 showed an increase of 1.0 percentage point per year (P < .001). Between 2004 and 2010, there was an unadjusted increase of 0.3 percentage point per year (P < .05). After adjustment for maternal age, hospital bed size, US Census region, expected source of payment, and clinical factors, trends were largely unchanged.
      Table 2Deliveries, primary cesarean deliveries, attempted labor, and successful labor among women with no previous cesarean
      YearDeliveries with no previous cesarean delivery

      (95% CI)

      (sample size)
      Primary cesarean deliveries

      (95% CI)

      (sample size)
      Deliveries with attempted labor

      (95% CI)

      (sample size)
      Successful labor

      (95% CI)

      (sample size)
      19903,601,000

      (3,336,000–3,867,000)

      (27,692)
      606,000

      (554,000–659,000)

      (4671)
      3,362,000

      (3,113,000–3,610,000)

      (25,900)
      2,995,000

      (2,768,000–3,222,000)

      (23,021)
      19913,543,000

      (3,289,000–3,796,000)

      (27,781)
      607,000

      (543,000–671,000)

      (4627)
      3,297,000

      (3,064,000–3,531,000)

      (25,957)
      2,936,000

      (2,729,000–3,143,000)

      (23,154)
      19923,454,000

      (3,209,695–3,699,000)

      (26,230)
      579, 000

      (526,000–632,000)

      (4443)
      3,229,000

      (3,001,000–3,458,000)

      (24,523)
      2,875,000

      (2,670,000–3,080,000)

      (21,787)
      19933,567,000

      (3,143,000–3,990,000)

      (23,909)
      583,000

      (480,000–686,000)

      (3925)
      3,338,000

      (2,948,000–3,729,000)

      (22,370)
      2,984,000

      (2,653,000–3,315,000)

      (19,984)
      19943,459,000

      (3,178,000–3,739,000)

      (28,238)
      547,000

      (487,000–606,000)

      (4490)
      3,233,000

      (2,974,000–3,492,000)

      (26,449)
      2,912,000

      (2,679,000–3,144,000)

      (23,748)
      19953,353,000

      (3,088,000–3,619,000)

      (26,091)
      519, 000

      (468,000–571,000)

      (3975)
      3,141,000

      (2,893,000–3,389,000)

      (24,561)
      2,834,0000

      (2,611,000–3,057,000)

      (22,116)
      19963,372,000

      (3,085,000–3,659,000)

      (27,798)
      529,000

      (475,000–583, 000)

      (4167)
      3,158,000

      (2,887,000–3,429,000)

      (26,225)
      2,842,000

      (2,598,000–3,087,000)

      (23,631)
      19973,355,000

      (3,108,000–3,602,000)

      (29,725)
      523,000

      (464,000–582,000)

      (4482)
      3,144,000

      (2,915,000–3,374,000)

      (27,946)
      2,832,000

      (2,631,000–3,033,000)

      (25,243)
      19983,488,000

      (3,220,000–3,756,000)

      (30,631)
      546,000

      (490,000–601,000)

      (4672)
      3,251,000

      (3,004,000–3,497,000)

      (28,719)
      2,942,000

      (2,720,000–3,165,000)

      (25,959)
      19993,373,000

      (3,085,000–3,661,000)

      (28,906)
      522, 000

      (469, 000–576,000)

      (4554)
      3,148,000

      (2,879,000–3,418,000)

      (26,977)
      2,850,000

      (2,610,000–3,090,000)

      (24,352)
      20003,290,000

      (3,006,000–3,574,000)

      (31,301)
      532,000

      (479,000–584, 000)

      (5087)
      3,062,000

      (2,794,000–3,330,000)

      (29,186)
      2,759,000

      (2,514,000–3,004,000)

      (26,214)
      20013,364,000

      (3,069,000–3,660,000)

      (31,568)
      604,000

      (541,000–666,000)

      (5566)
      3,100,000

      (2,831,000–3,369,000)

      (29,246)
      2,761,000

      (2,517,000–3,004,000)

      (26,002)
      20023,453,000

      (3,170,000–3,735,000)

      (30,684)
      638, 000

      (576,000–700,000)

      (5549)
      3,160,000

      (2,899,000–3,421,000)

      (28,367)
      2,814,000

      (2,585,000–3,044,000)

      (25,135)
      20033,487,000

      (3,160,000–3,814,000)

      (29,280)
      674, 000

      (597,000–751,000)

      (5662)
      3,194,000

      (2,891,000–3,497,000)

      (26,797)
      2,813,000

      (2,555,000–3,071,000)

      (23,618)
      20043,577,000

      (3,251,000–3,903,000)

      (33,784)
      738,000

      (667,000–809, 000)

      (7216)
      3,253,000

      (2,958,000–3,549,000)

      (30,537)
      2,839,000

      (2,575,000–3,102,000)

      (26,568)
      20053,469,000

      (3,154,000–3,783,000)

      (33,608)
      753,000

      (679,000–827,000)

      (7466)
      3,133,000

      (2,848,000–3,419,000)

      (30,275)
      2,716,000

      (2,463,000–2,969,000)

      (26,142)
      20063,513,000

      (3,181,000–3,845,000)

      (33,805)
      732,000

      (657,000–806,000)

      (7459)
      3,174,000

      (2,871,000–3,477,000)

      (30,387)
      2,781,000

      (2,510,000–3,052,000)

      (26,346)
      20073,516,000

      (3,172,000–3,860,000)

      (33,540)
      781,000

      (696,000–866,000)

      (7586)
      3,179,000

      (2,866,000–3,493,000)

      (30,202)
      2,735,000

      (2,463,000–3,007,000)

      (25,954)
      20083,499,000

      (2,714,000–4,284,000)

      (13,712)
      769,000

      (586,000–952,000)

      (3019)
      3,180,000

      (2,462,000–3,898,000)

      (12,508)
      2,730,000

      (2,120,000–3,340,000)

      (10,693)
      20093,374,000

      (2,617,000–4,131,000)

      (12,553)
      755,000

      (582,000–929,000)

      (2814)
      3,051,000

      (2,364,000–3,737,000)

      (11,366)
      2,619,000

      (2,023,000–3,214,000)

      (9739)
      20103,338,000

      (2,602,000–4,075,000)

      (11,663)
      769, 000

      (598,000–940, 000)

      (2619)
      3,017,000

      (2,340,000–3,694,000)

      (10,534)
      2,569,000

      (1,996,000–3,143,000)

      (9044)
      Total72,444,000

      (70,513,000–74,375,000)

      (572,499)
      13,307,000

      (12,868,000–13,746,000)

      (104,049)
      66,807,000

      (65,034,000–68,579,300)

      (529,032)
      59,137,000

      (57,595,000–60,679,000)

      (468,450)
      CI, confidence interval.
      Simon. Trends in primary cesarean and labor. Am J Obstet Gynecol 2013.
      Figure thumbnail gr1
      Figure 1Primary cesarean delivery percentage among those with no prior cesarean
      Unadjusted percentage of women with a primary cesarean delivery among those with no previous cesarean delivery, 1990-2010.
      Simon. Trends in primary cesarean and labor. Am J Obstet Gynecol 2013.
      Table 3Yearly percentage point change in delivery type among women with no previous cesarean
      VariableYear groupsUnadjusted (95% CI)Adjusted (95% CI)
      All adjusted models are adjusted for maternal age (greater than or less than 35 years), hospital bed size (less than 50, 50-99, 100-199, 200-299, 300-499, 500-999, or 1000 or more beds), Census geographic region (Northeast, Midwest, South, and West), expected source of payment (private insurance, Medicare, Medicaid, uninsured, other/unknown), preterm delivery, multiple gestation, hypertension, diabetes, large for gestational age, intrauterine growth restriction, and fetal anomalies. Attempted labor models and primary cesarean delivery models are also adjusted for placenta previa, genital herpes, and breech presentation
      Primary cesarean delivery
      1990-1999−0.2
      P < .05
      (−0.3 to −0.1)
      −0.3
      P < .01
      (−0.4 to −0.2)
      1999-20041.0
      P < .01
      (0.8–1.2)
      1.0
      P < .01
      (0.8–1.2)
      2004-20100.3
      P < .05
      (0.1–0.6)
      0.3
      P < .001.
      (0.1–0.5)
      Attempted labor
      1990-19980.0 (−0.1 to 0.1)0.1
      P < .05
      (0.0–0.2)
      1998-2005−0.4
      P < .01
      (−0.5 to −0.3)
      −0.3
      P < .01
      (−0.4 to −0.2)
      2005-20100.1 (−0.2 to 0.3)0.1 (−0.2 to 0.3)
      Labor success
      1990-19980.2
      P < .01
      (0.1–0.3)
      0.3
      P < .01
      (0.2–0.4)
      1998-2010−0.5
      P < .01
      (−0.5 to −0.4)
      −0.4
      P < .01
      (−0.5 to −0.3)
      CI, confidence interval.
      Simon. Trends in primary cesarean and labor. Am J Obstet Gynecol 2013.
      a All adjusted models are adjusted for maternal age (greater than or less than 35 years), hospital bed size (less than 50, 50-99, 100-199, 200-299, 300-499, 500-999, or 1000 or more beds), Census geographic region (Northeast, Midwest, South, and West), expected source of payment (private insurance, Medicare, Medicaid, uninsured, other/unknown), preterm delivery, multiple gestation, hypertension, diabetes, large for gestational age, intrauterine growth restriction, and fetal anomalies. Attempted labor models and primary cesarean delivery models are also adjusted for placenta previa, genital herpes, and breech presentation
      b P < .05
      c P < .01
      d P < .001.
      Of deliveries by women without previous cesarean delivery, estimates for deliveries undergoing labor ranged from 3,017,000 in 2010 to 3,362,000 in 1990 (Table 2). The attempted labor rate reached a high of 93.7% (95% CI, 93.3–94.2%) in 1997 and a low of 90.3% (95% CI, 89.6–91.0%) in 2005 (Figure 2). Joinpoint regression identified 2 significant joinpoints, 1998 and 2005. The unadjusted trends between 1990 and 1998 and between 2005 and 2009 were not significant (P > .05) (Table 3). Between 1998 and 2005, the rate of attempted labor declined an average of 0.4 percentage point per year (P < .001). After adjustment for factors described in previous text, the significance and size of the marginal yearly effects changed slightly. The adjusted rate of attempted labor increased an average of 0.1 percentage point per year between 1990 and 1998 (P < .01) and declined 0.3 percentage point per year between 1998 and 2005.
      Figure thumbnail gr2
      Figure 2Unadjusted labor attempt and labor success percentages among women with no previous cesarean
      Unadjusted percentage of women without previous cesarean delivery who labor during delivery (attempted labor) and unadjusted percentage of women without previous cesarean delivery who labor who have a successful labor (vaginal delivery), 1990-2010.
      Simon. Trends in primary cesarean and labor. Am J Obstet Gynecol 2013.
      The labor success rate for women with no previous cesarean delivery peaked at 90.5% (95% CI, 90.0–91.0%) in 1999 and was at its lowest rate of 85.2% (95% CI, 83.9–86.3) in 2010. Joinpoint regression identified a single joinpoint in 1998 (Figure 2). The unadjusted labor success rate for women with no previous cesarean delivery increased on average 0.2 percentage point per year between 1990 and 1998 (P < .001). Between 1998 and 2010, the unadjusted rate of labor success declined on average 0.5 percentage point per year (P < .001). After adjustment for factors described in the previous text, the marginal yearly effects changed slightly. The adjusted labor success rate increased 0.3 percentage point per year between 1990 and 1998 (P < .001) and decreased 0.4 percentage point per year between 1998 and 2010.
      Joinpoint analysis of only single, term deliveries yielded similar results for all trends, with the exception that the joinpoint (or change in trend) was found in 1999, rather than 1998, for labor success. Regardless of whether 1998 or 1999 was used to represent the change in trend, the unadjusted and adjusted marginal effects for single, term deliveries were similar to those found in analysis of the trends for all deliveries in both the earlier and later time periods.
      Similarly, analysis including codes for fetal distress and fetal heart rate abnormalities as indicators of labor increased the rate of labor and decreased the rate of labor success between 1 and 3 percentage points per year, but the trends were largely unchanged with the following exceptions. The joinpoints for both labor and labor success found in 1998 moved to 1999. Also, an additional joinpoint was identified for labor success in 2004, which changed the rate of decline from 0.8 percentage point per year prior to 2004 to 0.3 percentage point per year after 2004.

      Comment

      This study suggests that between 1990 and 1999, the rate of primary cesarean delivery declined 0.2 percentage point per year and then increased more than 1 percentage point per year until 2004. These trends appear similar to those found from the Vital Statistics system, with the exception that the primary cesarean rate from Vital Statistics reached its nadir in 1996-1997, rather than in 1999 as observed in the NHDS.
      • MacDorman M.
      • Declercq E.
      • Menacker F.
      Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.
      • Menacker F.
      • Curtin S.C.
      Trends in cesarean birth and vaginal birth after previous cesarean, 1991-99. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      In general, NHDS provides slightly higher estimates than Vital Statistics.
      • MacDorman M.
      • Declercq E.
      • Menacker F.
      Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.
      • Menacker F.
      • Curtin S.C.
      Trends in cesarean birth and vaginal birth after previous cesarean, 1991-99. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      For example, NHDS yielded a primary cesarean rate of 17.1% in 1991, whereas the rate from Vital Statistics was 15.9%.
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • Ventura S.J.
      • Menacker F.
      • Kirmeyer S.
      Births: final data for 2004. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
      After 2004, when Vital Statistics can no longer be used to track the primary cesarean delivery rate, the rate continued to increase, although at a slower rate of approximately 0.4 percentage point per year. These trends were not explained by changes in patient or hospital characteristics available in the NHDS.
      Changes in the primary cesarean delivery rate resulted from both changes in the rates of attempted labor and labor success. Between 1998 and 2005, the rate of attempted labor rate among women with no previous cesarean delivery declined approximately 0.4 percentage point per year. Additionally, the labor success rate declined an average of 0.5 percentage point per year between 1998 and 2010. The trends in attempted labor and labor success are similar to those found for births by women who have had prior cesarean deliveries,
      • Uddin S.F.
      • Simon A.E.
      Rates and success rates of trial of labor after cesarean delivery in the United States, 1990-2009.
      suggesting that practice pattern changes occurred across all deliveries, rather than being specific to 1 type of delivery.
      The percentage point changes in attempted labor and labor success rates are not large. However, because the average number of births among women with no prior cesarean between 1998 and 2005 was approximately 3,438,000 per year, just the decline in the labor attempt rate alone represents an average yearly increase of approximately 13,000 additional cesarean deliveries. Similarly, the yearly decline of 0.5% in labor success represents a yearly increase of approximately 16,000 additional cesarean deliveries. However, since 2005 the rate of labor attempts did not change, whereas the labor success rate continued to decline at 0.5% per year. Therefore, the continued increase in the primary cesarean delivery rate since 2005 was driven by the decline in the labor success rate.
      The overall number of cesarean deliveries in the United States increased by an average of 60,421 cesarean deliveries each year between 1998 and 2005.
      • Martin J.
      • Hamilton B.
      • Ventura S.
      • Osterman M.
      • Wilson E.
      • Mathews T.
      Births: final data for 2010.
      Hence, the decline in the rate of labor attempts among women with no prior cesarean delivery accounted for approximately 21.5% of the increase (13,000 cesarean births per year) between 1998 and 2005, whereas the decline in the success rate of labor among women with no previous cesarean delivery constituted approximately 26.5% of the increase in cesarean deliveries during these years (16,000 cesarean deliveries per year).
      Since 2005, the decline in labor success has become an even more important part of the overall increase in cesarean deliveries. The overall number of cesarean deliveries nationally increased by an average of approximately 40,000 cesarean births per year between 2005 and 2008.
      • Martin J.
      • Hamilton B.
      • Ventura S.
      • Osterman M.
      • Wilson E.
      • Mathews T.
      Births: final data for 2010.
      Of these, the decline in labor success accounted for nearly 40% of this change.
      It is unclear why changes in the labor attempt rate and the labor success rate have occurred. Both rates are likely influenced by many factors. Our results did not change after adjusting for clinical factors available in the NHDS. However, factors exist that are not measured in the NHDS. One study showed that the increase in the primary cesarean delivery rate in Nova Scotia, Canada, between 1988 and 2000 could be attributed to changes in maternal characteristics such as obesity and parity. With the exception of age, these characteristics were not available in NHDS.
      • Joseph K.S.
      • Young D.C.
      • Dodds L.
      • et al.
      Changes in maternal characteristics and obstetric practice and recent increases in primary cesarean delivery.
      Nonetheless, given that our results were robust to adjusting for available clinical factors, the possibility exists that trends may be due to changes in physician practices or patient preferences. Indeed, nonclinical factors have been shown to contribute to variation in the primary cesarean delivery rate.
      • Coonrod D.V.
      • Drachman D.
      • Hobson P.
      • Manriquez M.
      Nulliparous term singleton vertex cesarean delivery rates: institutional and individual level predictors.
      • Gregory K.D.
      • Korst L.M.
      • Platt L.D.
      Variation in elective primary cesarean delivery by patient and hospital factors.
      • Peipert J.F.
      • Hogan J.W.
      • Gifford D.
      • Chase E.
      • Randall R.
      Strength of indication for cesarean delivery: comparison of private physician versus resident service labor management.
      • Poma P.A.
      Effects of obstetrician characteristics on cesarean delivery rates. A community hospital experience.
      • Murthy K.
      • Grobman W.A.
      • Lee T.A.
      • Holl J.L.
      Association between rising professional liability insurance premiums and primary cesarean delivery rates.
      Among the many nonclinical factors to consider would be the release of relevant guidelines or important documents that might affect primary cesarean delivery rates. However, guidance from the American Congress of Obstetricians and Gynecologists, such as the guidelines released in 2000,
      was largely aimed at reducing the rates of primary cesarean, which we did not observe after 1999.
      This study has limitations. First, the NHDS is a sample survey and not a census of all deliveries in the United States, and there may be some error associated with survey procedures. Also, administrative data (ICD-9-CM codes) were used to identify women undergoing labor and those without previous cesarean delivery. This may misclassify women who underwent labor if labor-associated diagnoses are incorrectly recorded, and some evidence suggests labor attempts among those resulting in cesarean may not always be correctly coded.
      • Clayton H.B.
      • Sappenfield W.M.
      • Gulitz E.
      • et al.
      The Florida investigation of primary late preterm and cesarean delivery: the accuracy of the birth certificate and hospital discharge records.
      Similarly, early labor followed by planned cesarean could inflate the labor initiation rate. However, in either of these cases, the rates of misclassification would have had to change over time to affect the trends identified here. Also, the similarity of trends found using Vital Statistics and trends found using the NHDS during years when data were available from both sources supports the reliability of the NHDS data for this purpose.
      This study is the first to identify increases in the national primary cesarean delivery rate since 2004 and to track labor attempts and labor success among women with no previous cesarean delivery. Decreases in both the rates of labor attempts and labor success contributed significantly to the total increase in cesarean deliveries since 1999. From 1999 to 2004, both the rates of labor attempts and labor success among women with no previous cesarean declined. However, after 2004, the increases in the national primary cesarean delivery rate appear to result from the decline in the labor success rate.

      References

        • Martin J.
        • Hamilton B.
        • Ventura S.
        • Osterman M.
        • Wilson E.
        • Mathews T.
        Births: final data for 2010.
        National Vital Statistics Report. 2012; 61
        • National Institutes of Health Consensus Development Conference Panel
        National Institutes of Health Consensus Development conference statement: vaginal birth after cesarean: new insights March 8-10, 2010.
        Obstetrics and gynecology. 2010; 115: 1279-1295
      1. Oregon Health and Science University. Evidence-based Practice Center, United States. Agency for Healthcare Research and Quality. Vaginal birth after cesarean: new insights. Rockville, MD: Agency for Healthcare Research and Quality, US Department of Health and Human Services.

        • Martin J.A.
        • Hamilton B.E.
        • Sutton P.D.
        • Ventura S.J.
        • Menacker F.
        • Kirmeyer S.
        Births: final data for 2004. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
        Natl Vital Stat Syst. 2006; 55: 1-101
        • MacDorman M.
        • Declercq E.
        • Menacker F.
        Recent trends and patterns in cesarean and vaginal birth after cesarean (VBAC) deliveries in the United States.
        Clin Perinatol. 2011; 38: 179-192
        • Menacker F.
        • Curtin S.C.
        Trends in cesarean birth and vaginal birth after previous cesarean, 1991-99. National vital statistics reports: from the Centers for Disease Control and Prevention, National Center for Health Statistics.
        Natl Vital Stat Syst. 2001; 49: 1-16
        • Joesch J.M.
        • Gossman G.L.
        • Tanfer K.
        Primary cesarean deliveries prior to labor in the United States, 1979-2004.
        Matern Child Health J. 2008; 12: 323-331
      2. Cunningham FG, Williams JW. Williams obstetrics. New York: McGraw-Hill, Medical.

        • Clark E.A.
        • Silver R.M.
        Long-term maternal morbidity associated with repeat cesarean delivery.
        Am J Obstet Gynecol. 2011; 205: S2-S10
        • Spong C.Y.
        • Berghella V.
        • Wenstrom K.D.
        • Mercer B.M.
        • Saade G.R.
        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. 2012; 120: 1181-1193
        • Barber E.L.
        • Lundsberg L.S.
        • Belanger K.
        • Pettker C.M.
        • Funai E.F.
        • Illuzzi J.L.
        Indications contributing to the increasing cesarean delivery rate.
        Obstet Gynecol. 2011; 118: 29-38
        • Zhang J.
        • Troendle J.
        • Reddy U.M.
        • et al.
        Contemporary cesarean delivery practice in the United States.
        Am J Obstet Gynecol. 2010; 203: 326.e1-326.e10
        • Uddin S.F.
        • Simon A.E.
        Rates and success rates of trial of labor after cesarean delivery in the United States, 1990-2009.
        Matern Child Health J. 2013; 17: 1309-1314
        • National Center for Health Statistics
        National Hospital Discharge Survey—2008. Public Use Data File Documentation.
        National Center for Health Statistics, Hyattsville, MD2010
        • Dennison C.F.
        • Pokras R.
        Design and operation of the National Hospital Discharge Survey 1988 Redesign.
        National Center for Health Statistics, Hyattsville, MD2000
        • Gregory K.D.
        • Korst L.M.
        • Gornbein J.A.
        • Platt L.D.
        Using administrative data to identify indications for elective primary cesarean delivery.
        Health Serv Res. 2002; 37: 1387-1401
        • Henry O.A.
        • Gregory K.D.
        • Hobel C.J.
        • Platt L.D.
        Using ICD-9 codes to identify indications for primary and repeat cesarean sections: agreement with clinical records.
        Am J Public Health. 1995; 85: 1143-1146
      3. StataCorp. Survey data. StataCorp, College Station, TX2009
      4. National Cancer Institute. Joinpoint software; 2011.

        • Pokras R.
        Trends in hospital utilization: United States, 1965-86. Vital and Health Statistics Series 13.
        National Center for Health Statistics, Hyattsville, MD1989
        • Joseph K.S.
        • Young D.C.
        • Dodds L.
        • et al.
        Changes in maternal characteristics and obstetric practice and recent increases in primary cesarean delivery.
        Obstet Gynecol. 2003; 102: 791-800
        • Coonrod D.V.
        • Drachman D.
        • Hobson P.
        • Manriquez M.
        Nulliparous term singleton vertex cesarean delivery rates: institutional and individual level predictors.
        Am J Obstet Gynecol. 2008; 198: 694.e1-694.e11
        • Gregory K.D.
        • Korst L.M.
        • Platt L.D.
        Variation in elective primary cesarean delivery by patient and hospital factors.
        Am J Obstet Gynecol. 2001; 184 (discussion 32–4): 1521-1532
        • Peipert J.F.
        • Hogan J.W.
        • Gifford D.
        • Chase E.
        • Randall R.
        Strength of indication for cesarean delivery: comparison of private physician versus resident service labor management.
        Am J Obstet Gynecol. 1999; 181: 435-439
        • Poma P.A.
        Effects of obstetrician characteristics on cesarean delivery rates. A community hospital experience.
        Am J Obstet Gynecol. 1999; 180: 1364-1372
        • Murthy K.
        • Grobman W.A.
        • Lee T.A.
        • Holl J.L.
        Association between rising professional liability insurance premiums and primary cesarean delivery rates.
        Obstet Gynecol. 2007; 110: 1264-1269
      5. American College of Obstetricians and Gynecologists: Task Force on Cesarean Delivery Rates. Evaluation of cesarean delivery. American College of Obstetricians and Gynecologists, Washington, DC2000
        • Clayton H.B.
        • Sappenfield W.M.
        • Gulitz E.
        • et al.
        The Florida investigation of primary late preterm and cesarean delivery: the accuracy of the birth certificate and hospital discharge records.
        Matern Child Health J. 2013; 17: 869-878