Uterine stretch

Overdistension of the uterus as a PTB risk has been exemplified clin­ically by the decrease in the mean age of spontaneous delivery to 35 weeks in twins and 30 weeks in quadruplets. Additionally, women diagnosed with polyhydramnios and unicornuate uterus are also at increased risk of sPTB. In vitro, induced mechanical stretch of uterine myometrium causes increases in gap junction proteins such as connexin (Cx)-26 and Cx-43 (24), IL-8, and oxytocin receptor (OTR) expression. This leads to mitogen-activated protein kinase (MAPK) pathway activation (25), and upregulating cyclooxygenase (COX)-2 activity (26) terminating with local prostaglandin release causing increased contractility of the uterine muscle.