After the inclusion and exclusion process the final cohort comprised 3,850 women (Fig. 1). The majority of women (80%) answered their questionnaires 1–2 years after surgery: 786 (20%) at 6 months, 1,642 (41.8%) at 1 year , and 1,510 (38.2%%)at 2 years. Of the 3,856 women. 3,618 had had a hysterectomy and 238 a hysteroscopic procedure. As described above, the hysterectomy group was divided into two subgroups so a valid comparison with the hysteroscopy group was possible. The cut-off value was set according to the mean uterine size. In the GynOp register, uterine size is estimated in a gynaecological examination prior to the surgical intervention by palpation of the uterus, and is reported in terms of gestational weeks (GW) as small, normal, or 6, 8, 10, 12 or 14 GW, etc. A normal-sized uterus is considered a uterus at 4 GW. Thus the women were classified into three groups: group 1 comprised those with hysterectomy and ≤8 GW, group 2 those with hysterectomy and >8 GW, and group 3 all those with hysteroscopy. The mean uterine sizes of groups 1, 2 and 3 were 5.3 GW (95% CI 5.2–5.4 GW), 13.3 GW (95% CI 13.2–13.5 GW) and 5.3 GW (95% CI 5.0–5.6 GW), respectively. This classification is somewhat arbitrary with regard to LUTS symptoms since there is probably no difference clinically between uterine sizes 8 GW and 9 GW.
We also tested classifiers other than the mean uterine size. A receiver operating characteristic curve was created to determine a possible uterine size threshold for predicting LUTS. The best accuracy (area under the curve 0.52) was noted for 9.5 GW, indicating that uterine size is a poor prognostic factor for postoperative LUTS.
The basic preoperative characteristics of the women are shown in Table 1. Uterine size, age, BMI, and parity were similar in group 1 and group 3. Uterine size was significantly larger in group 2 than in groups 1 and 3. Group 2 had had fewer gynaecological surgery procedures than groups 1 and 3. Further analysis revealed that women in group 2 had had fewer tubal ligations and lesser cervical surgery (dysplasia) than women in groups 1 and 3.
The data regarding urinary symptoms are presented in Table 2. There were no differences between groups 1 and 3. Of women with a larger uterus (group 2), 8.0% reported urinary leakage after hysterectomy, and of those with a smaller uterus (group 1), 11.8% reported leakage (p < 0.001). Of women in group 2, 27.9% reported urgency before surgery compared with 17.7% in group 1 and 11.2% in group 3 (p < 0.001 in both cases). One year after surgery this result was reversed.: only 6.7% of women in group 2 reported urgency (a fourfold decrease), a rate lower than in group 1 (11.4%, p < 0.001) and group 3 (11.6% p = 0.004).
In the multiple regression analysis uterine size was not associated with the postoperative occurrence of LUTS in groups 1 and 3 (odds ratio, OR, 0.97, 95% CI 0.89–1.06, p = 0.567, for incontinence; OR 0.97, 95% CI 0.89–1.05, p = 0.485, for urgency; Fig. 2). In group 2 (>8 GW), an increase in uterine size of 2 GW had a slight protective effect against LUTS (OR 0.93, 95% CI 0.88–0.98, p = 0.011, for incontinence; OR 0.94, 95% CI 0.88–0.99, p = 0.03), for urgency).
The results of analysis of outcomes regarding LUTS according to urinary symptoms reported before surgery are shown in Table 3. There was no difference between groups 1 and 3 with regard to the presence of urinary incontinence before surgery. After surgery, the proportion of women in group 1 reporting de novo urinary incontinence was higher than in group 3 (7.6% vs. 3.2%, p = 0.015). This was also found in the multivariate analysis, which showed that hysteroscopy reduced the risk of de novo incontinence (OR 0.41, 95% CI 0.17–0.82, p = 0.023) more than hysterectomy (Fig. 2). Of women with a small uterus (group 1), 7.6% reported de novo urinary incontinence, a significantly higher proportion than among women with a large uterus (group 2, 4.2%, p < 0.001). If incontinence was present before surgery, the risk of incontinence was significantly higher after hysteroscopy than after hysterectomy (OR 7.49, 95% CI 2.17–30.54, p = 0.0026). Moreover, a high proportion of women (58.6%) with a uterus >8 GW reported relief of urinary leakage 1 year after surgery.
Analysis of urgency revealed no difference between groups 1 and 3 in the frequency of de novo urgency 1 year after surgery (Table 4). The risk of still having bothersome urgency after surgery was higher after hysteroscopy than after hysterectomy (OR 2.67, 95% CI 1.04–6.99, p = 0.042). Group 2 had a lower rate of de novo urgency than groups 1 and 3 (p < 0.001 and p = 0.015). Among women with symptoms present before surgery, 28.6% of those in group 1 had a significant decrease in urgency postoperatively (95%CI 23.7–34.1) compared with 48.4% of those in group 3 (95% CI 32.0–65.2, p = 0.038). An even larger proportion of women in group 2 had a decrease in urgency after surgery: 85.5% reported relief of urgency (p < 0.001 compared with both groups 1 and 3).
The results were further evaluated with regard to the mode of hysterectomy in the total cohort and within each group. There were no significant differences in the frequencies of urinary symptoms before and after hysterectomy among those who underwent abdominal, laparoscopic and vaginal hysterectomy (data not shown). In the patients in this study undergoing hysterectomy, by far the greatest proportion underwent abdominal hysterectomy (67.6% of all procedures); vaginal hysterectomy accounted for 25.8% and laparoscopic only 6.6% of procedures. Vaginal hysterectomy was more common in group 1 (42.2%).