Are left‐handed women at increased risk of endometriosis?

A recent study indicated that left-handed women have more than twice the risk of developing breast cancer before reaching the menopause than right-handed women 1. As a potential explanation, the authors suggest the existence of a prenatal intrauterine hormonal exposure that determines both cerebral lateralization and risk of breast cancer. The hypothesis that increased concentrations of estrogens during pregnancy increase the probability of future occurrence of breast cancer was previously discussed. Women prenatally exposed to diethylstilbestrol (DES) are more frequently left-handed 2. In the same population, the risk for breast cancer is increased only for the subset of estrogen receptor-positive cases, but the excess risk of 40% has not been found to be statistically significant 3. The rate of endometriosis is greater among women exposed to DES in utero (relative risk 1.8, 95% confidence interval 1.2–2.8) 4. However, women exposed in utero to DES also have a greater risk of cervical stenosis, and the incidence of cervical stenosis is increased even further if they have undergone cryocautery or conization; endometriosis, associated with chronic pelvic pain, is also a common finding in women with stenosis of the external cervical os 5. We have conducted a study with the aim to assess the association between left-handedness and incidence of endometriosis. From October 2006 to October 2011, patients with a history of pelvic laparoscopy with or without histologically proven endometriosis and seeking medical consultation in an endometriosis referral center were interviewed regarding their innate hand preference. They were classified into left-handed and non-left-handed groups. Their medical files were reviewed and both groups were compared for demographic characteristics, gynecological history and family history of endometriosis. Comparison of proportions was made with an exact Fisher's test and comparisons of means with a Student's t-test or the Wilcoxon test in case of heteroscedasticity. We included 932 patients in the study, 477 (51.1%) with and 455 (48.81%) without a histologically confirmed history of endometriosis. The occurrence of a family history of endometriosis (p < 10−9), a younger age of menarche (p = 0.004), a shorter duration of menstrual cycle (p < 10−9), a longer duration of menstrual bleeding (p < 10−3), and the presence of uterine retroversion (p < 10−9) were significantly higher in the endometriosis group as shown in Table 1. A total of 79 (8.4%) patients were left-handed, 57 (11.7%) in the group with endometriosis and 22 (4.8%) in the group without endometriosis (p < 10−4). Left-handed women seem therefore to have a significantly increased risk of developing endometriosis with an odds ratio of 2.67 (95% confidence interval 1.57–4.67). This appears to be the first time this association has been reported, i.e. that left-handed women have an increased risk of developing endometriosis. A unique origin related to high intrauterine levels of estrogens could be advocated and should be investigated by a study with wider scope.