[2] The fetal membranes are four of six accessory organs developed by the conceptus that are not part of the embryo itself, the other two are the placenta, and the umbilical cord.

[4] The function of this microvillous surface is associated with a densely-packed glycocalix with anionic binding sites; these are thought to be involved with intra-amnionic lipid synthesis.

[11] The human allantois is a caudal out-pouching of the yolk sac, which becomes surrounded by the mesodermal connecting stalk or body-stalk.

The amnion is in contact with the amniotic fluid and ensures structural integrity of the sac due to its mechanical strength.

At the end of gestation, a 'weak zone' develops in the fetal membrane overlying the cervix due to collage remodelling.

The chorion expresses chemicals that balance synthesis and metabolism of these prostaglandins to ensure that the myometrium is not activated pre-term.

This enzyme converts biologically inactive cortisone into active cortisol, another chemical vital for fetal maturation and labour initiation.

Key indicators of preterm birth are short cervical length and a raised cervical-vaginal fetal fibronectin concentration.

[15] Structural abnormalities such as areas of where collagen has degraded, known as microfractures, have been observed in the amniotic membrane layer.

However, if the inflammatory response increases above this level it can have dangerous and potentially fatal effects for the mother and child.

[15] Sterile inflammation can be caused by both microbial infection and non-infectious factors, such as senescence of fetal membranes.

[20] Once the telomeres have reached a critical length the cell can no longer divide and can hence cause telomere-dependent replicative senescence.

This should occur naturally at term (37 weeks), as it is an important factor to increase the inflammatory environment in the uterus to initiate parturition.

However, fetal membrane senescence can be accelerated by oxidative stress and hence, stimulate sterile inflammation to occur prior to term; consequently, causing preterm birth.