Factors implicated in the initiation of human parturition in term and preterm labor: a review

Abstract

After accommodating the pregnancy for an average of 40 weeks, the uterus expels the fetus, the placenta and the membranes through the birth canal in a process named parturition. The absolute sequence of events that trigger and sustain human parturition are not yet fully clarified. Evidence suggests that spontaneous preterm and term labor seem to share a common inflammatory pathway. However, there are several other factors being involved in the initiation of human parturition. Placental corticotropin releasing hormone production seems to serve as a placental clock that might be set to ring earlier or later determining the duration of pregnancy and timing of labor. Estrogens do not cause contractions but their properties seem to capacitate uterus to coordinate and enhance contractions. Cytokines, prostaglandins, nitric oxide and steroids seem also to induce ripening by mediating remodeling of the extracellular matrix and collagen. Infection and microbe invasion resulting in chorioamnionitis also represents a common cause of early preterm labour. This review provides an overview of all these factors considered to be implicated in the initiation of human parturition.

Myometrial cytokines and their role in the onset of labour

“…Progesterone and progesterone receptor The withdrawal of progesterone (P4) has long been 231:3 hypothesised to be the trigger of labour, with supportive evidence from animal models, in particular sheep and goat where a fall in P4 and a concurrent increase in oestradiol precedes the onset of labour (Ravanos et al 2015). This does not apply to humans, as there is no decline in circulating maternal P4 levels before labour.…”

“…It also exerts an anti-inflammatory action via inhibition of cytokine production and immune cell migration into the uterus and suppresses the transcription of genes that promote contractility. Interestingly, in human labour, a functional impairment in P4 receptor levels have been reported near term, which may reverse P4's suppressive actions, therefore, promoting myometrium's sensitivity to contract (Ravanos et al 2015).…”

α-Tocopherol Potentiates the Cervical Resistance Decreasing Effects of COX Inhibitors in Pregnant Rats: The Putative Role of Cyclooxygenase-2 Inhibition

“…Several studies have investigated the exact role of PGs in cervical remodeling. PGE 2 increased the activity of collagenase in the human cervix (Osmers et al, 1991) and the inflammatory response, which characterizes cervical ripening and remodeling (Ravanos et al, 2015). PGF 2a enhanced the synthesis of hyaluronic acid and glycosaminoglycans (Murota et al, 1977).…”

Regulation of inflammation by lipid mediators in oral diseases

“…PGF 2 α plays an important reproductive role in pregnancy by regulating luteolysis (De Rensis et al , ), partially through upregulation of Slit/Robo expression (Zhang et al , ). It has strong procontraction effects on the uterus (Ravanos et al , ). Elevated PGF 2 α levels are associated with endometriosis (Ahmad et al , ; Rakhila et al , ).…”