Approximately 15 million preterm neonates are born annually and more than 1 million die from subsequent complications within the following 5 years. Adverse outcomes related to prematurity span a spectrum that includes neurodevelopmental (e.g., neurocognitive impairment, cerebral palsy, hearing impairments, and intellectual or motor disabilities), pulmonary (e.g., bronchopulmonary dysplasia) and ophthalmologic (e.g., retinopathy of immaturity) disorders that contribute to lifelong disability.
In a Danish cohort study women with endometriosis had an increased risk of preterm birth before 37 gestational weeks overall (adjusted hazard rate [aHR] 1.6, 95% confidence interval [CI] 1.3-1.9) and very preterm birth before 32 gestational weeks (aHR 1.8, 95% CI 1.1-2.9) compared with women without endometriosis. Medically indicated preterm birth was more prominent in women with endometriosis in deliveries before 37 gestational weeks (aHR 2.4, 95% CI 1.8-3.2) whereas spontaneous labor contractions were more common before 32 gestational weeks (aHR 2.2, 95% CI 1.1-4.5) in women with endometriosis compared with women without endometriosis. Further, in the analyses restricted to women with a histologically verified diagnosis of endometriosis, the results were strengthened overall and showed that women with endometriosis had an increased risk of PPROM before 32 gestational weeks (aHR 3.49, 95% CI1.36-8.98).
The endometrial-myometrial junctional junction (EMJ), is related to peristaltic-like movements in the non-pregnant uterus. Hyperperistalsis and dysperistalsis of uterus underlie many important disorders such as dysmenorrhea, infertility, endometriosis, implantation failure and preterm birth. The maximum thickness of EMJ in patients with endometriosis is significantly greater than in patients without endometriosis (6.5 ± 1.9 mm vs 4.8 ± 1.0 mm.
The major proteins for uterine contraction of the non-pregnant uterus are Oxytocin (OT) and the oxytocin receptor (OTR). The expression level of OTR in the fundus region of the EMJ is positively associated with the severity of dysmenorrhea in endometriosis group (r = 0.870, p < 0.05). Comparing to normal uteri, the expression of OTR in the secretory phase was significantly higher in the endometriosis uteri (p < 0.05). In the fundus of endometriosis uteri, OTR expression was significantly higher in both the proliferative and secretory phases (p = 0.045 and 0.028, respectively).
Given the critical role oxytocin receptors and the increased thickness of the EMJ in women with endometriosis it is not surprising that oxytocin antagonist such as atosiban are effective in the treatment of PTL.