Obstetrician explains: three stages of labour

The big moment has finally arrived! But what happens now? Specialist obstetrician, Dr Nick Walker explains the fine print. 

Many people are familiar with the general idea of 'the rule of threes' – whether referring to events auspicious or otherwise, or simply to divide a phenomenon into logically separate and mentally manageable compartments. Maternity researchers and caregivers have applied this idea to pregnancy, and we have described three ‘trimesters’ of pregnancy each of which is around 14 weeks long and each roughly corresponding to various biologically significant milestones. We have also described three ‘stages’ of active labour. In this article we’ll explore the three stages of labour, what you might expect as well as what you might not!

BEFORE THE FIRST STAGE OF LABOUR 

In the final weeks of your pregnancy, in the absence of any concerns, and assuming your pregnancy checks do not reveal any health issues for you or your baby – a waiting game is being played. Your uterus will often be practising for labour by self-stimulating muscular contractions (eponymously named ‘Braxton-Hicks contractions’ after the surname of the obstetrician who first thought to label them) and your baby will be exerting head-first pressure on the internal end of your cervix. By gradual degrees, these two processes gently soften and open the cervix, converting it from a firm and closed tunnel into a soft and open ring. It is at this stage possible for an internal examination to determine how ready your body is for labour, and some patients and caregivers may wish for this to be done to allow an estimate to be given on the proximity of labour.

Adding to the examination, your Lead Maternity Carer (LMC) and you may agree to proceed with a so-called cervical sweep: physical stimulation of the cervix and loosening of the sac membranes in an attempt to initiate labour. Whether by this technique or by spontaneous onset, your cervix and uterine muscles begin to manufacture a special group of bioactive molecules called ‘prostaglandins’ (named because in the early days of biomedical research they were first isolated and purified from prostate glands!), and as the level of prostaglandins steadily increases your body becomes closer and closer to the first stage of labour.

Just prior to the official first stage of labour, women usually experience a period known as the ‘latent phase’ of labour. Distinct from the active phase of labour, the latent phase is characterised by a contraction pattern that is non-regular and unpredictable. Perhaps best considered as an intermediate place between Braxton-Hicks contractions and definite labour contractions, the latent phase is highly variable between pregnancies and can last up to 24 hours at the end of your first pregnancy. Typically in a woman who has had at least one previous baby, the latent phase is much shorter, and may last only 30 minutes! What's important to mention at this point, is that the various stages of labour, including the latent phase, are defined by the measurable parameters of cervical dilation (openness) and uterine contractions. Regularity, frequency and duration are key rather then subjective levels of pain or intensity.  So, after some time in the latent phase, you will then enter the first stage of labour...

THE FIRST STAGE OF LABOUR

The first stage of labour is defined as the interval between a cervical dilation of three centimeters and ten centimeters. The entry point of three centimeters is relatively arbitrary, and some institutions prefer to set the starting point at four centimeters to account for any subjective error in what ought to be an objective measure. At any rate, in almost all cases whereby the baby’s head has caused the cervix to be several centimeters dilated, contractions will be regular and long-lasting, with a resting interval of two to four minutes. 

A positive feedback loop is established as each contraction of the main muscular body of the uterus draws the cervix backwards over the baby’s head at the same time as pushing the head forwards. A good way to picture this action is when you don a turtleneck sweater by pushing your head whilst pulling the fabric in the opposite direction. When the cervix stretches further, contractions are maintained and even intensified throughout the first stage of labour, which – as defined above – finishes at 10 centimeters (full) dilation. 

The narrowest and easiest fit for the baby to fit through the birth canal corresponds to a roughly circular shape that could be drawn from an imaginary line running downwards from behind the baby’s ear, across the nape of the neck, upwards behind the opposite ear and over the top of the cranium back to the beginning point behind the initial ear. The diameter of this circle measures around nine and a half centimeters, corresponding to the ten centimeters required for the cervix to draw past the widest point of the head.

Understanding this concept is key to understanding why the first stage of labour can happen quickly or slowly, and may complete entirely or not complete during your birth process. With a well-positioned, chin-tucked-down (flexed) head, the cervix draws easily and smoothly over the rounded part of the leading point of the baby’s head, and the efficiency of this leads to a shorter first stage of labour.  Conversely, if the baby’s head is ‘deflexed’ and is presenting a more oval and elongated profile, the cervix has a more difficult shape to accommodate with a longer overall circumference, and the first stage of labour will be longer. This unfavourable and inefficient set-up is commonly known as ‘posterior position’. The best way to imagine this is to think of an oval rugby ball passing through a netball hoop: an end-on position goes through much easier than a side-on!

THE SECOND STAGE OF LABOUR

The second stage of labour is defined across the interval between the final and full dilation of the cervix and the birth of the baby. By now the baby’s head has completely exited the uterus and is snug in the vagina, waiting to be pushed through the curtain of muscles that make up the pelvic floor.

The pushing force at this stage can now come from two sources: the uterine contractions which are still occurring, and the addition of your own efforts of bearing down. At this time your caregivers will encourage you, cheer you on and do their best to keep your efforts as strong and efficient as possible.

If you have an epidural, the pressure feedback you feel from pushing may be blunted somewhat, and it is typical to therefore allow an epidural to wear low or even wear off in order to minimise this. During this second stage, the baby’s head position still plays a key role in determining the ‘ease’ of the birth. Well-flexed positions present a smaller diameter to fit through the gap in the pelvic floor muscles, while larger oval-shaped posterior positions are more difficult.

The other difficulty, which varies from person to person, is the curvature of the vagina the baby must travel through. You can only push in a straight line, though the baby ends up going in a ‘J’ shape pathway downwards then upwards.

Luckily, during the second stage of labour, it becomes possible (if required) for an obstetrician to help with delivering the baby. While you might push as hard as possible, a difficult position or foetal stress may necessitate an assisted vaginal delivery with either a vacuum cup suction device or obstetric forceps.

The decision as to which are used and why, should be carefully explained prior to helping you have your baby. It is really important to still try as hard as you can, to help your obstetrician and your baby, as the combined efforts of both of you will make sure of a safe outcome.  

THE THIRD STAGE OF LABOUR: AFTER THE BABY IS BORN

Congratulations! The start of the third stage of labour is my personal favourite part of pregnancy. The brand new baby meets their parents, the new parents meet their baby, and the combined wonder and relief of the moment make it truly special. There is just a tiny bit to go, a few more contractions, to separate and expel the placenta. The placenta is a disc-shaped clump of tissue which has faithfully linked you and your baby from the beginning, encouraging your body to accept and nurture the pregnancy and passing almost all of that which it is given, onwards to your baby. Having happily completed this task, and having been disconnected from your baby at the cutting of the umbilical cord, by one final contraction it is gently pushed off the wall of the uterus where it was secured and follows the same path taken minutes earlier by the baby it has helped to create. Once the placenta has birthed, the third stage of labour is complete.

Following the third stage of labour there is still plenty to get done for you and your caregivers: repairing any injuries by suturing, cleaning away body fluids, having food and drink, and a lot of paperwork. Your baby will begin suckling and within an hour or so the first nappies will need changing. The stages of labour have ended, but the stages of parenting have only just begun.

Dr Nick Walker is a specialist obstetrician working in public practice at National Women’s Hospital and private practice in Auckland. He divides his time between these roles and helping his wife care for their four children.