Home Pregnancy & Birth What causes labour to start? – Understanding the birth process

What causes labour to start? – Understanding the birth process


For centuries, philosophers, doctors and birth supporters have been writing about an incredible event called Childbirth. In the 21st century there has been must research and debate around the topic along with advancement in medical technology. This along with the ever increasing skill of Doctors and midwives today has had a profound impact on decreasing maternal and infant morbidity and mortality, however has also a part to play in the increasing rate of caesarean sections and instrumental births.
Normal birth should be promoted empowering women to have belief that their bodies are fit for purpose. One of the things that needs to be understood to enable this is the process of birth and why women’s bodies do the things they do.

A normal human pregnancy can last anywhere from 38-42 weeks from the first day of a woman’s last period. This can vary from woman to woman, some women will go a few days over 42 weeks without any problems at all. Many midwives with recommend closer monitoring though at this stage as the placenta begins to mature. There are no studies to suggest that there is a significant risk of placental failure before 43 weeks of pregnancy. Because of this, it may be wrong to suggest a pregnancy is ‘post dates’ before 42 weeks of pregnancy.

No one is sure of the exact trigger for labour in under normal circumstances however some of the following ideas have been in circulation for some time:

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.

How labour starts varies from woman to woman. Some will experience a release of the waters that are surrounding the baby. This occurs when a hole forms in the sac which the baby has been growing in. This may then be followed immediately by the womb contracting but not always. Sometimes this can happen hours or a few days later. Some women will not experience a release of any water but will begin to feel their womb tighten or ache periodically throughout the day.



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