Objective
The purpose of this study was to compare the risk of surgically treated stress urinary incontinence (SUI) and pelvic organ prolapse (POP) in relation to mode of delivery and age at first childbirth.
Study Design
This was a cohort study. Data from the Swedish Medical Birth Register on women with only cesarean delivery (n = 30,880 women) or only vaginal delivery (n = 59,585 women) were compared with the Swedish Patient Register to calculate incidence rates and hazard ratios (95% confidence interval [CI]) for SUI and POP surgery.
Results
In analyses that were stratified by age, vaginal delivery consistently increased the risks of SUI and POP surgery. Among vaginally delivered women who were ≥30 years old, incidence rates of POP surgery were 13.8 (95% CI, 12.7–15.1), and for younger women were 6.4 (95% CI, 6.0–6.8) per 10,000 person-years. Exclusion of instrumental vaginal delivery did not alter the conclusions.
Conclusion
Increasing age at first delivery increased the risk of subsequent SUI and POP surgery after both vaginal and cesarean delivery.
Advanced maternal age at first delivery is now a widespread phenomenon across industrialized countries. From 1973-2007, the mean age at first birth in Swedish women has increased from 24-28 years. In large urban areas, the change has been particularly notable; in the capital, the mean age at first delivery increased from 25-30 years during the same period. In the United States, the number of first births per 1000 women increased by 36% among women 35-39 years old and by 70% in age group 40-44 years between 1991 and 2001. Postponing first childbirth has been shown to increase the risks of unfavorable perinatal outcomes, the incidence of breast cancer, and cardiovascular diseases.
Childbirth is considered widely to be an established risk factor for pelvic floor disorders later in life, and increasing maternal age at childbirth has been associated with increased risks of levator muscle injury, anal sphincter laceration, and stress urinary incontinence. However, most studies rely on hospital-based study populations with short duration of follow up. Furthermore, the associations between advancing age, stress urinary incontinence, and, in particular, pelvic organ prolapse are poorly characterized. Thus, it remains to be determined whether increasing maternal age at first childbirth influences the long-term risk for pelvic floor sequelae. We performed a nationwide, matched cohort study that was based on high-quality Swedish healthcare registers to assess the influence of maternal age at first childbirth on the risk of surgical stress urinary incontinence and pelvic organ prolapse later in life.
Materials and Methods
Study population
We linked 3 Swedish population-based registries by the use of the individually unique national registration numbers assigned to all Swedish residents at birth or immigration. The Swedish Medical Birth Register, which is kept by the National Board of Health and Welfare, contains obstetrics data for >98% of all women delivered in Sweden since 1973. Within the Medical Birth Register, we identified a cohort of women who had their first child by cesarean delivery from January 1973 through December 1982 and who thereafter (if multiparous) gave birth only by cesarean delivery. Study subjects in this cohort were individually matched by birth year of the mother, county, and calendar time of birth with women with their first and all subsequent childbirths by vaginal delivery (if multiparous). We included childbirths from January 1, 1973, to the end of the observation period (December 31, 2004). A total of 33,167 women who had cesarean deliveries at first and all subsequent childbirths fulfilled the inclusion criteria and were matched individually with 63,229 women who had only vaginal childbirths. After the initial matching procedure, 5931 women were excluded, which left 90,465 subjects whose data were eligible for analyses. Exclusion criteria included (1) diagnosis of both vaginal and cesarean delivery (274 women), (2) multiple pregnancy (2060 women), (3) whether stress urinary incontinence or pelvic organ prolapse surgery preceded or were performed in the same year as first birth (6 women), (4) death before December 31 of the year of the first birth (36 women), and (5) lack of either being exposed or nonexposed in matching strata after exclusion were performed (3555 women).
Both cohorts subsequently were linked to the Swedish National Patient Register, which contains data for individual hospital discharges. The register was established in 1964, and national coverage was achieved in 1987. Correct coding is achieved in 98% of records in the register, with a <1% yearly loss to registration.
Data collection
From the Medical Birth Register, we retrieved information on delivery mode characterized as either vaginal or cesarean delivery, instrumental vaginal delivery (forceps or vacuum extraction), maternal age at delivery, total parity, diabetes mellitus at entry of pregnancy, gestational age, infant birthweight, and fetal head circumference. Information on death before the end of the study was obtained from the Cause of Death Register.
We used specific codes from the Swedish classification of operations and major procedures for 1973-1996 and 1997-2004 to identify pelvic floor surgical procedures in the Swedish Patient Register. Our primary outcome measures were surgical procedures for stress urinary incontinence and pelvic organ prolapse, which included Kelly sutures, Kennedy sutures, abdominal and laparoscopic Burch colposuspensions, Stamey procedures, Ingelman-Sundberg plasty, intravaginal slingplasty, suburethral slings, and tension-free vaginal tapes (operation codes 6355, 6356, 6358, 7470, 7471 for 1973-1996, and LEG00, LEG10, LEG20, LEG96 and KDG10-40 for 1997-2004). Pelvic organ prolapse surgeries were categorized as anterior repair, posterior repair, Manchester procedure, abdominal sacrocolpopexy, vaginal sacrospinous fixation, abdominal and vaginal enterocele obliteration, colpocleisis and hysterectomy for pelvic organ prolapse (operation codes 4840, 4841, 4844, 4935, 7120, 7121, 7460-7464, 7466, 7469 and 7541 for 1973-1996 and LEF00, LEF03, LEF10-50, LEF53, LEF96, LFE20, JHB 40, JHB96, JFJ00, JGC00, JGC01 for 1997-2004). From the Patient Register, we also obtained information about age at surgery and calendar time of surgery.
Statistical analysis
Crude and age-specific incidence rates for stress urinary incontinence and pelvic organ prolapse surgery were calculated separately as the number of events per 10,000 person-years with 95% confidence interval (CI) based on the Poisson distribution. Women contributed person-time to the study from the January 1 of the year after the first delivery until the first occurrence of incontinence surgery, pelvic organ prolapse surgery, death, or end of the observation period (Dec. 31, 2004). Risks of stress urinary incontinence or pelvic organ prolapse surgery related to delivery mode and age at first delivery were estimated with Cox’s proportional-hazards models and were adjusted for obstetrics factors. Age-specific hazard ratios (HRs) were dichotomized in <30 vs ≥30 years old at first birth and were in further analyses that were also estimated through stratification in 5-year bands.
Parity was categorized in 1, 2, and ≥3 deliveries. Other variables were dichotomized into whether the woman had ever had pregestational or gestational diabetes mellitus, a gestational age of ≥40 weeks, and/or an infant with a birthweight of ≥4 kg or with a head circumference of ≥38 cm. Effect modification of variables was evaluated by type-3 test before being entered in the Cox proportional hazard model. Age at last delivery showed neither effect modification of clinical interest nor confounding of the results and therefore was not included in the final regression model. To address the potential confounding effects of instrumental vaginal delivery, subgroup analyses were performed with the exclusion of women who had ever delivered by vacuum extraction (n = 8335) or forceps delivery (n = 287). Statistical analyses were performed with SAS software (version 9.1; SAS Institute Inc, Cary, NC). The study was approved by the Research Ethics Committee at Karolinska Institutet, Stockholm, Sweden.
Results
During an inclusion period of 10 years, 90,465 women were followed from first birth over an observational period that encompassed nearly 2.5 million person-years. Mean follow-up time was 27.1 years in the cesarean delivery cohort and 25.8 years in the vaginal delivery cohort. Cohort characteristics are presented in Table 1 . Mean age at last delivery did not differ between the cohorts, nor did time from last childbirth to pelvic organ prolapse surgery. Time from last birth to stress urinary incontinence surgery was, however, almost 3 years shorter in the vaginal birth cohort. These women were also 3 years younger at the time of stress urinary surgery compared with women who had stress urinary incontinence surgery in the cesarean delivery cohort.
| Characteristics | Vaginal delivery cohort | Cesarean delivery cohort |
|---|---|---|
| Persons included in analysis, n | 59,585 | 30,880 |
| Parity, n a | 2.1 ± 1.0 | 1.8 ± 0.9 |
| Instrumental vaginal delivery, n (%) | 8622 (14.3) | – |
| Persons with stress urinary incontinence surgery, n (%) b | 718 (4.5) | 136 (1.7) |
| Persons with pelvic organ prolapse surgery, n (%) b | 1295 (8.1) | 58 (0.7) |
| Age at first delivery, y a | 25.8 ± 5.0 | 27.1 ± 5.6 |
| Age at last delivery, y a | 30.4 ± 5.1 | 30.6 ± 5.4 |
| Time from last birth to stress urinary incontinence surgery, y a | 14.3 ± 7.5 | 17.1 ± 6.3 |
| Time from last birth to pelvic organ prolapse surgery, y a | 15.8 ± 8.0 | 15.5 ± 7.4 |
| Age at stress urinary incontinence surgery, y a | 46.3 ± 7.5 | 49.0 ± 7.3 |
| Age at pelvic organ prolapse surgery, y a | 49.0 ± 8.4 | 47.9 ± 8.6 |
a Data are given as mean ± SD;
Table 2 shows incidence rates and hazard ratios in relation to mode of delivery and age at first childbirth. For both delivery groups, the incidence rates per 10,000 person-years of stress urinary incontinence surgery were higher in the older age category. Women who were ≥30 years old at first vaginal birth had an increased incidence rate per 10,000 person-years for pelvic organ prolapse surgery (rate, 13.9; 95% CI, 12.8–15.2) when compared with younger women (rate, 6.4; 95% CI, 6.0–6.8).
| Age category, y | ||||
|---|---|---|---|---|
| 13-29 | ≥30 | |||
| Variable | Incidence rate a | Hazard ratio b | Incidence rate a | Hazard ratio b |
| STRESS URINARY INCONTINENCE SURGERY | ||||
| Crude | ||||
| Cesarean delivery | 1.4 (1.1–1.7) | 1.0 (Reference) | 2.4 (1.9–3.1) | 1.0 (Reference) |
| Vaginal delivery | 4.0 (3.6–4.4) | 3.0 (2.3–3.9) | 6.1 (5.4–7.0) | 2.4 (1.8–3.3) |
| Adjusted c | ||||
| Cesarean delivery | 1.1 (0.8–1.5) | 1.0 (Reference) | 2.0 (1.4–2.8) | 1.0 (Reference) |
| Vaginal delivery | 3.2 (2.3–4.2) | 3.0 (2.3–4.0) | 4.9 (3.5–6.9) | 2.4 (1.8–3.4) |
| PELVIC ORGAN PROLAPSE SURGERY | ||||
| Crude | ||||
| Cesarean delivery | 0.6 (0.4–0.9) | 1.0 (Reference) | 1.0 (0.7–1.5) | 1.0 (Reference) |
| Vaginal delivery | 6.4 (6.0–6.8) | 8.8 (6.2–12.4) | 13.8 (12.7–15.1) | 12.5 (8.1–19.1) |
| Adjusted c | ||||
| Cesarean delivery | 0.4 (0.2–0.6) | 1.0 (Reference) | 0.8 (0.5–1.2) | 1.0 (Reference) |
| Vaginal delivery | 3.4 (2.6–4.2) | 7.4 (5.2–10.5) | 9.7 (7.6–12.4) | 11.0 (7.1–16.9) |
a Per 10,000 person-years; data are given as incidence rate (95% confidence interval);
b Data are given as ratio (95% confidence interval): adjusted for parity (1, 2, ≥3); diabetes mellitus at pregnancy; head circumference ≥38 cm, gestational length ≥40 weeks of gestational length, and infant birthweight ≥4 kg;
c Estimated for the covariate pattern parity (n = 1), diabetes mellitus at pregnancy (no), head circumference of ≥38 cm (no), gestational length of ≥40 weeks of gestational length (no), and infant birthweight of ≥4 kg (no).
In the age category 13-29 years, women with vaginal childbirths had a 3-fold increased risk of stress urinary incontinence surgery compared with women who delivered by cesarean delivery (HR, 3.0; 95% CI, 2.3–4.0, Table 2 ). Among women ≥30 years old at first childbirth, the corresponding risk was more than doubled among vaginally delivered women (HR, 2.4; 95% CI, 1.8–3.4). For pelvic organ prolapse, the risk of having surgery after vaginal childbirths was >7 times that of cesarean delivery among women 13-29 years old (HR, 7.4; 95% CI, 5.2–10.5). Among women aged ≥30 years, the risk of pelvic organ prolapse surgery was 11 times increased among women with vaginal deliveries (HR, 11.0; 95% CI, 7.1–16.9) when compared with women delivered by cesarean. When we excluded women with vaginal instrumental deliveries, the age-categorized risk estimates for stress urinary incontinence and pelvic organ prolapse surgery among vaginally delivered women did not change substantially (data not shown).
Analyses of stress urinary incontinence and pelvic organ prolapse surgery stratified by age at first childbirth are shown in Table 3 . Compared with cesarean delivery, vaginal delivery among women ≤35 years old was associated with at least a 3-fold increased risk of stress urinary incontinence surgery. For pelvic organ prolapse surgery, there was an even stronger effect of vaginal delivery; a markedly increased risk was especially obtained among women 30-34 years old (HR, 18.1; 95% CI, 9.1–35.6) and 35-38 years old (HR, 15.9; 95% CI, 7.1–35.4) at first childbirth.
| Age category, y | |||||||
|---|---|---|---|---|---|---|---|
| Surgery | ≤19 | 20-24 | 25-29 | 30-34 | 35-38 | ≥39 | Overall |
| n | 7817 | 29,606 | 29,699 | 16,120 | 5659 | 1564 | 90,465 |
| Stress urinary incontinence | |||||||
| Event: cesarean vs vaginal delivery, n | 6 vs 51 | 32 vs 207 | 38 vs 236 | 31 vs 169 | 24 vs 48 | 5 vs 7 | 136 vs 718 |
| Cesarean delivery a | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) |
| Vaginal delivery | |||||||
| Crude a | 3.6 (1.3–9.4) | 2.9 (1.9–4.6) | 3.2 (2.2–4.6) | 3.4 (2.2–5.2) | 1.4 (0.8–2.5) | 2.6 (0.6–10.2) | 2.7 (2.2–3.2) |
| Adjusted a , b | 3.6 (1.3–9.6) | 3.0 (1.9–4.7) | 3.2 (2.2–4.7) | 3.3 (2.1–5.2) | 1.5 (0.8–2.7) | 2.4 (0.6–9.8) | 2.9 (2.3–3.5) |
| Pelvic organ prolapse | |||||||
| Event cesarean vs vaginal delivery, n | 1 vs 57 | 14 vs 272 | 19 vs 462 | 9 vs 337 | 7 vs 139 | 8 vs 28 | 58 vs 1295 |
| Cesarean delivery a | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) | 1.0 (Reference) |
| Vaginal delivery | |||||||
| Crude a | 20.5 (2.8–151) | 7.3 (4.2–12.7) | 9.9 (6.2–16.0) | 18.0 (9.1–35.6) | 15.9 (7.1–35.4) | 3.6 (1.4–8.8) | 10.1 (7.7–13.2) |
| Adjusted a , b | 16.9 (2.3–126) | 6.0 (3.4–10.6) | 8.4 (5.2–13.6) | 16.4 (8.3–32.5) | 13.7 (6.1–30.8) | 3.0 (1.2–7.4) | 9.2 (6.9–12.1) |
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