As mothers everywhere will tell you, labour is definitely no easy feat. Every experience is different, and depending on the type of pregnancy, the duration of labour can vary between 2 and 18 hours. After nine months of pregnancy, the wait is finally over and the human body readies itself for the delivery of a new life. But how does the body prepare for such an undertaking? The communication between the mother and foetus’s body, along with various molecules and chemicals turns out to be key in beginning this process.
Labour is initiated through a change in the uterus from what is known as an anti-inflammatory state to a pro-inflammatory state. This essentially means that the body harnesses the power of the immune system during labour and causes the release of certain molecules and chemicals. This switch to turn on the immune system is caused by the activation of an important gene complex known as NFkB. Human labour involves complex communication between the placenta, foetal lungs, foetal membranes and the mother’s uterus – which are all geared towards activating NFkB. The question is – what starts it all off?
The foetus must communicate its stage of development to the mother in order to initiate labour. The baby’s lungs are one of the last organs to development, and as they reach the final stages of maturity, they secrete pulmonary surfactant, a detergent-like agent, which prevents lungs from collapsing during exhalation. Studies on mice have shown that a component of this surfactant helps to promote labour by up-regulating NFkB and other pro-inflammatory molecules in the mother’s uterus and triggering contractions. In fact, one of these pro-inflammatory molecules (known as prostaglandin) can be used in the form of a gel to induce labour in some mothers that have gone past their due date, or who have developed potentially threatening conditions such as pre-eclampsia.
The muscle layer within the mother’s uterus is known as the myometrium. During pregnancy, this muscle lies dormant. During delivery however, the contraction of the muscle becomes essential. Muscle contractions rely on electrical impulses that spread through them – and the propagation of these impulses is only achieved by proteins on the surface of the cell known as gap junctions. These gap junctions, whilst normally absent, are widely expressed during the late phase of pregnancy – a single muscle cell can express over 1000 copies. It is these proteins that are the gatekeepers of communication between the foetus and the mother’s uterus.
However, it is important that this muscle does not contract prematurely and cause early contractions. A hormone known as CRH (corticotropin releasing hormone) is released to prevent this from occurring – the production of which is controlled by the placenta.
Hormones are key to the process of labour, so it is not a surprise that the pregnant mother a specimen of hormonal firepower. Fluctuating hormones – such as the reduction of progesterone and the increase in oestrogen – signal the oncoming of labour itself. Another hormone, oxytocin, is known as the bonding hormone. Its levels stay constant throughout pregnancy. However, in labour, the oxytocin receptor (that binds to oxytocin) increases hugely. This means that oxytocin is able to bind to its receptor, induce the creation of prostaglandin and initiate muscle contraction in the uterus.
Understanding how labour initiates in humans has proved almost impossible due to the obvious ethical issues surrounding human foetal experimentation. Sadly, premature labour affects about 10% of pregnancies and is common in pregnancy related diseases such as pre-eclampsia, and intra amniotic infection. The prize for unravelling the complex initiating mechanism of labour is the potential to help prevent premature birth, which is the most common cause of neonatal death worldwide. Whilst the intricacies of the labour process are a fascinating topic, perhaps it’s best not to mention these to a mother in labour – our best bet is she won’t be thanking you for your insight!
Syed Asaad Qadri is studying for an MSc in Reproductive and Developmental Biology