Objective
The objective of the study was to estimate the risk for postoperative adhesions and intestinal obstruction after cesarean delivery and to estimate whether the rate remains stable over time.
Study Design
Women who had the aforementioned diagnoses in the Swedish Hospital Discharge Registry were linked to the Swedish Medical Birth Registry. Women with diagnoses increasing the risk for adhesions were excluded. More than 900,000 women were investigated. Risks were calculated and were adjusted for age, parity, body mass index, and smoking.
Results
Women delivered by cesarean delivery had an increased risk of adhesions: adjusted odds ratio, 2.1 (95% confidence interval, 1.8–2.4) and intestinal obstruction: adjusted odds ratio, 2.0 (95% confidence interval, 1.7–2.4). The number needed to harm was 360. Multiple caesarean deliveries increased the risk of adhesions. The risk did not increase over time.
Conclusion
The absolute risk of postoperative adhesions and intestinal obstruction after cesarean section are low but should be included when counseling women requesting cesarean delivery.
Postoperative adhesions are frequent sequelae of gynecologic open surgery. Epidemiologic studies show that around 5% of readmissions after gynecologic open surgery are due to adhesions. Apart from the need for repeat surgery, adhesions may cause infertility, intestinal obstruction, and chronic pelvic pain. There are only a few large studies available estimating the risk of adhesions after cesarean section. Existing knowledge point to a lower risk for intestinal obstruction after cesarean delivery than after gynecologic surgery, indicating a lower risk for adhesions.
The aim of this study was to evaluate the risk for postoperative adhesions and its most serious consequence intestinal obstruction after cesarean delivery in a large sample. A secondary aim was to evaluate whether the rate remained stable over time.
Materials and Methods
The Swedish Patient Register (PAR), kept by the National Board of Health and Welfare (Stockholm, Sweden) was used to identify women with a diagnosis of adhesions or intestinal obstruction, respectively. Using the personal identification number assigned to each resident in Sweden, the data were linked to the Swedish Medical Birth Registry (MBR), which is also kept by the National Board of Health.
The PAR contains information on diagnoses (1987-1996: International Classification of Diseases [ICD], ninth revision; 1997 and onward: ICD10) and operation codes of all in-patients admitted to any Swedish hospital. The MBR is kept by the National Board of Health and Welfare and contains medical information on nearly all deliveries in Sweden (coverage about 99%). Standardized record forms are used at all antenatal clinics, all delivery units, and at all pediatric examinations of newborn infants in the maternity ward. Information on maternal smoking and body mass index (BMI, kilograms per square meter) are prospectively recorded by the midwife at the first visit to the antenatal center. Copies of the standardized record forms are sent to the National Board of Health and Welfare where they are computerized.
Women were included if they were delivered between 1983 and 2004. The ICD9 codes 568 and 614 and ICD10 codes K66 and N736 were used to identify women with adhesions. The corresponding ICD codes used to identify women with intestinal obstruction were 560 (ICD9) and K56 (ICD10). For women who had been diagnosed more than once, only the first diagnosis was counted.
Cases were excluded if they had a previous diagnosis of peritonitis, appendicitis, ulcerative colitis, Crohn’s disease, salpingoophorectomy, exploratory laparotomy, laparoscopy, or salpingitis. The final case group consisted of women who had their first diagnosis of adhesions or intestinal obstructions more than 365 days after the last delivery and were not older than 60 years of age.
Odds ratios (ORs) were obtained using the Mantel-Haenszel (1959) procedure. Stratification was made for the women’s year of birth (2 year intervals), the year of the last delivery (1 year interval), the parity at the last delivery (previous deliveries plus 1), smoking at the last delivery (none, smoking <10 cigarettes per day, smoking ≥10 cigarettes per day), BMI at the last delivery (<20 kg/m 2 , 20-24.9 kg/m 2 , 25-29.9 kg/m 2 , ≥30 kg/m 2 ), and years of involuntary childlessness before the last delivery (0, 1-2, 3-4, ≥5). Approximate 95% confidence intervals (CIs) were calculated using the method proposed by Miettinen. Tests of homogeneity of the ORs across strata were based on weighted sums of the squared deviations of the stratum specific log ORs from their weighted means.
As a complement to the Mantel-Haenszel analyses, Cox analyses were performed to obtain hazard ratios for adhesions or intestinal obstruction after the first cesarean delivery (CD) vs the first vaginal delivery. These subanalyses included only women who experienced their first delivery between 1986 and 2004, a time period that was covered by the PAR registry. This subcohort was also used to produce Kaplan-Meier estimates.
The time for the study entrance was set to the first delivery. The time for the study exit was set at the date of the first diagnosis of adhesions or intestinal obstruction, respectively, the date of the 60th birthday, or at Dec. 31, 2004 (when the dataset was retrieved), depending on which event happened first.
Women with vaginal births before their first CD contributed with person-months to the vaginal births group before the first CD. After the first CD, however, all person-months were designated to the CD group. Adjustments were made for maternal age at the study entry (continuous variable, quadratic model), BMI (continuous), maternal smoking (yes/no), and years of involuntary childlessness at the study entry (the first delivery). The COX and the Kaplan-Meier analyses were performed using Gauss.
The study was approved by the Research Ethics Committee at Karolinska Institutet (Stockholm, Sweden).
Results
Table 1 displays descriptive statistics of women who were delivered during 1983-2004 and had a diagnosis of adhesions or intestinal obstruction, respectively, reported to the PAR in 1987-2005. The total number of births was 1,019,607, the number of women with the diagnosis of adhesions 1794 (1.8 per 1000) and intestinal obstruction 1389 (1.4 per 1000). Women who were delivered during the first part of the study period had a longer time of follow-up than had women who were delivered toward the end of the study period. Consequently, the proportion of women who were diagnosed with adhesions or intestinal obstruction, respectively, decreased with the year of the last delivery. Also, the proportion of women who were diagnosed with any of the aforementioned conditions increased with maternal age.
| Adhesions a | Intestinal obstruction a | Total population | |||
|---|---|---|---|---|---|
| Characteristic | n | Per thousand | n | Per thousand | n |
| Total n | 1794 | (1.8) | 1389 | (1.4) | 1,019,607 |
| Maternal year of birth | |||||
| Before 1950 | 129 | (2.9) | 187 | (4.3) | 43,839 |
| 1950-1959 | 901 | (3.2) | 720 | (2.6) | 281,636 |
| 1960-1969 | 670 | (1.5) | 426 | (1.0) | 434,318 |
| 1970 or later | 94 | (0.4) | 56 | (0.2) | 259,814 |
| Year of birth at last delivery | |||||
| 1983-1985 | 596 | (5.6) | 371 | (3.5) | 106,423 |
| 1986-1990 | 712 | (3.5) | 514 | (2.5) | 203,842 |
| 1991-1995 | 356 | (1.5) | 336 | (1.4) | 241,174 |
| 1996-2000 | 98 | (0.5) | 141 | (0.7) | 203,612 |
| 2001-2004 | 32 | (0.1) | 27 | (0.1) | 264,556 |
| Parity at last delivery | |||||
| 1 | 521 | (2.0) | 292 | (1.1) | 256,907 |
| 2 | 719 | (1.5) | 628 | (1.3) | 477,400 |
| 3 | 423 | (2.0) | 338 | (1.6) | 214,702 |
| ≥4 | 131 | (1.9) | 131 | (1.9) | 70,598 |
| Maternal smoking at last delivery (cigarettes/d) | |||||
| Not known | 226 | (1.6) | 209 | (1.5) | 139,100 |
| No smoking | 965 | (1.4) | 756 | (1.1) | 702,764 |
| <10 | 360 | (3.3) | 245 | (2.2) | 110,633 |
| ≥10 | 243 | (3.6) | 179 | (2.7) | 67,110 |
| Maternal BMI at last delivery, kg/m 2 | |||||
| Not known | 699 | (2.1) | 576 | (1.7) | 339,884 |
| <20 | 233 | (2.5) | 204 | (2.2) | 92,960 |
| 20-24.9 | 660 | (1.7) | 458 | (1.2) | 393,334 |
| 25-29.9 | 164 | (1.2) | 102 | (0.7) | 141,799 |
| ≥30 | 38 | (0.7) | 49 | (0.9) | 51,630 |
| Involuntary childlessness | |||||
| No | 1625 | (1.7) | 1270 | (1.3) | 964,861 |
| 1-2 years | 75 | (2.4) | 61 | (2.0) | 30,636 |
| 3-4 years | 47 | (3.7) | 26 | (2.0) | 12,774 |
| ≥5 years | 47 | (4.1) | 32 | (2.8) | 11,336 |
| Mode of delivery | |||||
| Vaginal births only | 1294 | (1.6) | 1023 | (1.2) | 831,758 |
| Vaginal and CDs | 209 | (2.2) | 159 | (1.7) | 94,863 |
| CD only | 291 | (3.1) | 207 | (2.2) | 92,986 |
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