Endometriosis is one of the challenges for women with pelvic pain and infertility. Chronic pelvic pain affects about 15% of women of childbearing age and reduces their quality of life . In the present study, the mean age of patients was 32.4 years, and the disease was highly severe in less than half of the cases, which is consistent with results of Khawaja et al . The infertility rate in women with endometriosis in the present study was 37.3%, which is consistent with the study of Radhika et al. . Bellelis et al. reported infertility rates as 31.5% and 40%, respectively.
This study aimed to explore the relationship between the severity of endometriosis symptoms (dyspareunia, dysmenorrhea, and chronic pelvic pain) and the spread of the disease. The results show that only the severity of dyspareunia is related to the stage of endometriosis, and the odds ratio of endometriosis was 0.24 in the absence of dyspareunia. In previous studies, many attempts have been made to clarify the association of the type and location of lesions and the spread of the disease with the severity and symptoms of the disease, which has had no consensus on results .
The growth of nerve fibers in ectopic implants is considered as the mechanism of severe pain in endometriosis [20-22]. According to Varecellini et al’s study , dysmenorrhea, as one of the most common symptoms of endometriosis, was associated with atypical and popular implants. Fedele et al.  reported the association of dysmenorrhea with advanced stages of endometriosis. Chapron et al. , showed that dysmenorrhea was associated with the size and depth of the lesions. However, in other studies, there was no relationship between menstrual pain and endometriosis , which shows that other factors cause this pain, and merely examining the appearance of implants can reveal the true nature of the disease.
In the present study, there was no relationship between dysmenorrhea and chronic pelvic pain , and disease severity. The results of this study are inconsistent with those of Varcellini et al. , who found a significant association of disease severity and dysmenorrhea with chronic pelvic pain. Although their estimated odds ratio for dysmenorrhea and chronic pelvic pain (1.33 and 1.01, respectively) was very close to 1 and does not indicate any strong correlation. A slight change in the sample volume possibility causes the missing of the confidence interval.
Results of the present study suggested that there is a significant relationship between dyspareunia and posterior DIE lesion, and has been strongly confirmed in other studies. Anatomically, the most stretched area during intercourse is the retro-cervical area , which indicates the organic nature of this pain. Anaf et al.  showed a histological relationship between nerves and endometriotic foci in retro-cervical nodules . Besides, Douglas stenosis was significantly associated with dyspareunia in the present study, which has been reported in almost all previous studies. Varcellini et al. reported a strong association between Douglas pouch lesions and dyspareunia .
Studies show that the association between ovarian endometriosis and dysmenorrhea has conflicting results. Although endometrioma was common among the patients in the present study (83.4%), no significant association was found between endometrioma and dysmenorrhea, which is consistent with the results of some researchers (Radhika et al. , Porpora et al. , Chapron et al. , and Koninckx et al ). In contrast, Muzii et al.  and Fedele et al.  showed thatthe association between endometrioma and pelvic pain was significant, which is inconsistent with the results of the present study.