Objective
The purpose of this study was to estimate the incidence of postpartum hemorrhage (PPH) in the United States and to assess trends.
Study Design
Population-based data from the 1994–2006 National Inpatient Sample were used to identify women who were hospitalized with postpartum hemorrhage. Data for each year were plotted, and trends were assessed. Multivariable logistic regression was used in an attempt to explain the difference in PPH incidence between 1994 and 2006.
Results
PPH increased 26% between 1994 and 2006 from 2.3% (n = 85,954) to 2.9% (n = 124,708; P < .001). The increase primarily was due to an increase in uterine atony, from 1.6% (n = 58,597) to 2.4% (n = 99,904; P < .001). The increase in PPH could not be explained by changes in rates of cesarean delivery, vaginal birth after cesarean delivery, maternal age, multiple birth, hypertension, or diabetes mellitus.
Conclusion
Population-based surveillance data signal an apparent increase in PPH caused by uterine atony. More nuanced clinical data are needed to understand the factors that are associated with this trend.
Postpartum hemorrhage (PPH) is a frequent complication of pregnancy and is among the most common causes of pregnancy-related death in the United States. Recent reports demonstrated a rising trend in severe maternal morbidity during US delivery hospitalizations that was attributable largely to the increased use of blood transfusions. In addition, data from Canada and Australia indicate recent increases in PPH rates and aggregate US data show that the percentage of women whose discharge records contained International Classification of Diseases, 9th Revision, Clinical Modification ( ICD-9-CM ) codes for PPH increased from 2.0% in 1993–1997 to 2.6% in 2001–2005.
For Editors’ Commentary, see Table of Contents
PPH is an etiologically heterogeneous event and not a diagnosis. The causes of PPH include poor uterine tone (uterine atony), retained placental tissue, abnormalities of placentation, genital tract trauma, and abnormalities of coagulation. A recent report documented that apparent increases in rates of PPH largely were due to an increase in the use of the ICD-9-CM code for uterine atony. As a first step to better understand the problem of PPH in the United States, we undertook a descriptive analysis of US population-based administrative hospital discharge data to examine trends in PPH, with special attention to the contribution of uterine atony and associated obstetric factors.
Materials and Methods
Data for this investigation were obtained from the Nationwide Inpatient Sample (NIS) for the years 1994–2006. The NIS is part of the Agency for Healthcare Research and Quality’s Healthcare Cost and Utilization Project. The details of the NIS have been described in detail elsewhere. Briefly, the NIS is the largest inpatient care database in the United States; after appropriate weighting, NIS data are intended to be representative of all patients who are admitted to US hospitals. During annual data collection by the Healthcare Cost and Utilization Project, all nonfederal community hospitals from participating states are stratified by rural/urban location, number of beds, region of the country, teaching status, and ownership. Within each stratum, a systematic random 20% sample of hospitals is drawn. The database contains ≤15 diagnosis fields and 15 procedure fields for each discharge; diagnoses and procedures are coded at the hospital at discharge with the ICD-9-CM codes. Because the NIS is available to the public and does not contain any personal identifying information, this investigation did not require approval by an institutional review board.
Except for age, the NIS does not collect individual demographic information, nor does it report obstetric characteristics for individual pregnancies, except those that can be translated to ICD-9-CM codes. As such, this analysis focuses on ICD-9-CM diagnosis codes for obstetric hemorrhage and coded characteristics of the delivery. Following the validated methods of Kuklina et al, we characterized delivery hospitalizations using a hierarchic algorithm based on ICD-9-CM diagnosis and procedure codes and diagnosis-related group codes.
There are 4 ICD-9-CM codes for PPH. Cases of uterine atony at delivery were identified by the 5-digit code 666.1X. All other PPH was identified by the PPH codes 666.0X (retained, trapped, or adherent placenta), 666.2X (delayed and secondary PPH), and 666.3X (postpartum coagulation defects). We collapsed the latter 3 codes (for cases of PPH not attributable to uterine atony) into a single category labeled “other hemorrhage.” Cesarean section delivery was identified by ICD-9-CM code 74.X, induction by 73.4, previous cesarean section delivery by 654.2X, and blood transfusions by 99.03 and 99.04.
We calculated rates as percentages of deliveries, plotted annual rates from 1994-2006, and assessed the significance of trends in rates by calculating orthogonal polynomial contrasts according to the methods of Fisher and Yates as described in the SUDAAN Example Manual . In an attempt to explain trends in rates, we used logistic regression to model uterine atony as a function of time, maternal age, induced labor, cesarean delivery, multiple birth, hypertension during pregnancy, diabetes mellitus during pregnancy, and hospital location and characteristics. We compared rates of uterine atony in 2006 with those in 1994 for each mode of delivery after age standardizing the 2006 rate to the age distribution of women who delivered in 1994. Finally, the odds of atony for each mode of delivery were calculated for 1994 and for 2006 with adjustment for age. All counts and proportions were weighted with the use of the weighting variables in the NIS that account for the complex sampling design. Hence, estimates are generalizable to the US population. All analyses were performed with SAS software (version 9.1; SAS Institute Inc, Cary, NC) and SAS-callable SUDAAN (version 9.0; RTI International, Research Triangle, NC).
Results
From 1994–2006, the NIS collected data on 10,481,197 delivery hospitalizations, which represented a weighted estimate of 51,674,542 delivery hospitalizations in the United States during that period; 2.7% of the women who were discharged after delivery during that period received a code for PPH. Three-fourths of these women were identified by the presence of the single code for uterine atony. Two of every 1000 women with a PPH code also had a code for blood transfusion at discharge. One in 4 women delivered by cesarean section, and 1 in 7 women had labor induction. Maternal characteristics of the population and the characteristics of the delivery hospitalizations were different between 1994 and 2006 ( Table 1 ). In 2006, women were older and more likely to use government insurance; they were more likely to deliver by cesarean section or after induction of labor, have a multiple gestation, and have pregnancies that were complicated by hypertension and diabetes mellitus. In 2006, women were less likely to have a vaginal birth when a previous birth occurred by cesarean section delivery.
| Characteristic | Percentage ± SE a | |
|---|---|---|
| 1994 (n = 3,791,724) | 2006 (n = 4,260,198) | |
| Age, y | ||
| <20 | 12.8 ± 0.4 | 10.5 ± 0.3 |
| 20-34 | 75.1 ± 0.2 | 75.4 ± 0.2 |
| >34 | 12.1 ± 0.3 | 14.2 ± 0.4 |
| Payer | ||
| Medicaid/Medicare | 38.7 ± 1.3 | 42.9 ± 1.3 |
| Private insurance | 53.0 ± 1.5 | 50.3 ± 1.6 |
| Self | 8.3 ± 0.8 | 6.8 ± 0.7 |
| Mode of delivery | ||
| Vaginal | 74.8 ± 0.3 | 67.0 ± 0.3 |
| Vaginal birth after cesarean | 4.0 ± 0.1 | 1.5 ± 0.1 |
| Repeat cesarean | 7.7 ± 0.1 | 13.5 ± 0.2 |
| Primary cesarean | 13.4 ± 0.2 | 18.1 ± 0.3 |
| Labor induction | 9.8 ± 0.4 | 16.3 ± 0.5 |
| Multiple birth | 1.4 ± 0.0 | 1.7 ± 0.0 |
| Hypertension b | 5.6 ± 0.1 | 8.1 ± 0.1 |
| Diabetes mellitus b | 3.4 ± 0.1 | 6.1 ± 0.1 |
a May not total to 100 because of rounding;
Between 1994 and 2006, the percentage of deliveries with a code for PPH increased by 26%, from 2.3% (85,954 deliveries) to 2.9% (124,708 deliveries; test of trend, P < .001; Figure 1 ). There was a parallel increase in PPH caused by atony during this same time period, from 1.6% (58,597 cases) to 2.4% (99,904 cases; P < .001). Delivery hospitalizations with PPH codes not caused by atony did not increase ( P > .05). Multivariable logistic regression with simultaneous adjustment for all variables that are given in Table 1 and hospital size, urban vs rural location, geographic region, and teaching status showed no significant effect of these variables on the change in the risk of PPH between 1994 and 2006.
The percentage of delivery hospitalizations with the ICD-9-CM code for uterine atony varied by the mode of delivery and whether pregnancy was induced ( Figure 2 ). The highest rate of uterine atony occurred among women whose labor was induced and who delivered vaginally. This was followed by women whose induction ended in cesarean delivery and women who had vaginal births without induction of labor. Women who had cesarean deliveries and did not have induced labor consistently had the lowest rates of PPH caused by atony. The percentage of women with a PPH code that indicated atony who also had a code for blood transfusion more than doubled between 1994 and 2006 (test of trend, P < .001; Figure 3 ).
