Is it the baby who decides it is time to come out or the womans body?

Wikipedia lists some factors.

There are an enormous number of factors that can be involved in premature birth.

I had a nephew born prematurely after his twin sister died in utero. The mother’s body couldn’t decide what to do.

I have always thought labour was triggered by some sort of hormone. I had also heard that the baby, through the release of a hormone, triggers labour. I just did a little very quick searching and found this which also suggests hormones trigger labour to start. It appears we really don’t know for sure though. The information below is taken from the Midwives Online website.

“It still is unclear what causes labour to begin, there are several theories. One is that the mother’s pituitary gland secretes oxytocin when the baby is fully developed and ready to be born. Oxytocin is the hormone that stimulates contractions.

For many years, it was believed that the mother’s body was responsible for starting labour. Some researchers now believe that the baby actually starts labour. The baby sends a signal to the mother’s body that causes labour to start. One theory is that the baby’s lungs secrete an enzyme when they are fully developed. This causes prostaglandins to be released into the mother’s system. The prostaglandins then trigger changes in the cervix and contractions. Another theory is that the baby’s adrenal glands send a signal to start labour. When the baby is ready to be born, the adrenal glands produce hormones. These hormones cause hormonal changes in the mother. These changes are responsible for the process that starts labour.

While there are many theories, no one really knows what triggers labour. This process remains a mystery. As research continues, the answer to this question may soon be answered.” (Midwives Online 2012).

I think it’s a combination of all three working in natural unison.. Watch the birth of a chicken egg.. You can’t expect an apple to taste it juiciest unless you leave it on the tree to ripen..