Obstetrics is the branch of medicine that deals with pregnancy and giving birth. Most women have uneventful pregnancies with no complications. It is after all a natural physiological event, but part of obstetric care is to try to identify and prevent problems occurring during pregnancy and labour that could otherwise affect the health of the mother and the unborn baby.

There are numerous complications of pregnancy that makes it desirable, or necessary, to either stop a labour that has started prematurely before the normal 40 weeks gestation, or to start one that has been delayed beyond this time.

Premature (pre-term) birth
Globally, it is estimated that 13 million babies are born prematurely each year. Premature, or pre-term birth, is one of the most common causes of death and disability in infants and there is an urgent need to unravel its causes, as the reasons behind it remains a mystery in many cases.

All sorts of techniques have been tried to halt a labour that has started too early. Most treatment involves the use of medications called tocolytic agents that are designed to stop the contractions of the uterus. They are particularly useful at postponing delivery giving the baby a chance to mature further or to enable the mother to reach a hospital with specialist facilities. 

Induction of labour
Labour is initiated or induced by obstetricians in situations where it is considered safer for the mother, or the unborn child, if the baby were to be removed from the womb.
 
Reasons for induction include pre-eclampsia (sudden, severe rise in blood pressure and kidney impairment), poor growth in the baby, or unexplained bleeding in the last phase of pregnancy, but the most common reason is a prolonged pregnancy.

After 42 – 43 weeks of pregnancy most doctors agree that the baby is more likely to experience problems, with an increased risk of death, or brain damage, if the pregnancy were to continue. Therefore labour is normally induced at around 42 weeks if it hasn’t already occurred naturally.

Biology of labour
To ensure treatments to delay or induce labour are as effective and as safe as possible it is necessary to understand the natural processes involved in labour and birth. Many of the hormonal changes that happen throughout the process are understood, but the actual trigger for labour is complex and remains somewhat elusive.

Childbirth can be divided into three main stages. The first stage of labour prepares and opens the cervix for the baby to pass through, the second stage is the actual birth of the baby and the third stage relates to the passing of the placenta. Oxytocin and prostaglandins are the main substances produced at the end of a pregnancy to initiate the key processes for labour and birth. 

Oxytocin is the hormone that drives the uterus to contract, pushing the baby down towards the cervix. While the release of prostaglandins set in motion the processes that soften the cervix, making it thinner, and encouraging it to open ready for the baby to pass through, they also make the uterus more sensitive to oxytocin.

At the start of labour, the pressure of the baby against the cervix sends a signal for more oxytocin to be released. This in turn stimulates more frequent and forceful contractions of the uterus that push the baby even harder against the cervix sending additional signals for the release of even more oxytocin. This intensifying cycle is broken once the baby is born and there’s no further pressure on the cervix.

However, as soon as the baby is born, the uterus continues to contract to expel the placenta and return to its pre-pregnant state as soon as possible. After the placenta is delivered the uterus should contract and become very firm.