Deep infiltrating endometriosis is associated with markedly lower body mass index: a 476 case-control study.

Background: An inverse association between BMI and endometriosis has been reported but remains controversial. We decided to evaluate the association between BMI and the different types of endometriosis, classified as superficial endometriosis (SUP), deep infiltrating endometriosis (DIE) and ovarian endometrioma (OMA).

Methods: From a prospective database of patients who underwent gynecological surgery between February 2005 and October 2008, we compared 238 patients with a histological diagnosis of endometriosis to 238 age- and smoking-status-matched controls using a prospective preoperative questionnaire and surgical data. Numerical variables means were compared for matched pairs, and non-parametric variables using Wilcoxon test. The Odds ratios for all types of endometriosis adjusted for confounding variables were computed according to predefined BMI groups [1(<18.5), 2 (≥18.5 and <22), 3(≥22 and <25), 4(≥25)], taking Group 3 as the reference population.

Results: BMI was significantly lower for all 238 patients (21.70 ± 3.7 versus 23.29 ± 4.1, P < 0.001), for 101 OMA patients (21.88 ± 3.8 versus 22.99 ± 4, P < 0.038), and for 97 DIE patients (21.35 ± 3.4 versus 23.35 ± 3.8, P < 0.001) compared with their own controls, but not for the 40 SUP patients. Patients in Group 1 had adjusted odds ratios as high as 3.3 [95% confidence interval (CI): 1.6-6.8] for DIE and 2.7 (95% CI: 1.1-6.8) for OMA; in Group 2, the adjusted oddd ratios were 2.6 (95% CI: 1.3-5.5) for DIE and 2.9 (95% CI: 1.5-5.4) for OMA.

Conclusions: Endometriotic patients have lower BMI than age- and smoking-status-matched controls, independent of confounding variables. Patients with the lowest BMI (<18.5) are at a high risk of DIE.