Stages of childbirth

Labour begins as a hormonal response, probably to triggers from the baby's adrenal gland. This prompts your uterus to start contracting. Your waters may break before this, or afterwards: every birth is different.

If you're induced (when labour's brought on medically), hormones are administered as a drip or a pessary inserted in your vagina to stimulate contractions.

Latent phase

This phase of pregnancy can last many days and the contractions are more intense, longer and more frequent versions of the Braxton-Hicks contractions that begin at around 26 weeks. Cervical effacement is the shortening and thinning of the cervix. It occurs during the closing weeks of pregnancy and is usually complete or near complete, by the end of latent phase. The sctor, nurse or midwife often performs a vaginal exam to  determine the degree of cervical effacement. A 'long' cervix implies that not much has been taken into the lower segment, and vice versa for a 'short' cervix. Latent phase ends with the onset of active first stage; when the cervix is about 3 cm dilated.

First stage: contractions

The first stage of labor starts classically when the effaced (thinned) cervix is 3 cm dilated. Each woman is different and so there is  variation in this point as some women may have active contractions prior to reaching this point whilst others may reach this point without regular contractions. The onset of actual labour is defined when the cervix begins to progressively dilate. Rupture of the membranes, or a 'bloody show' (talked about in signs of labour) may or may not occur at around this stage. Contractions allow your uterus to push the baby downwards and to pull the cervix upwards, allowing the exit to get bigger and bigger in preparation for your baby's head.

Uterine muscles form opposing spirals from the top of the upper segment of the uterus to its junction with the lower segment. During effacement, the cervix becomes incorporated into the lower segment of the uterus. During a contraction, these muscles contract causing shortening of the upper segment and drawing upwards of the lower segment, in a gradual expulsive motion. This draws the cervix up over the baby's head. The muscles then relax and the contraction fades, but the muscle fibres remain slightly shorter than they were before. The baby is pushed down a little further and the cervix stays open a little wider. Full dilatation is reached when the cervix is the size of the baby's head wich is  around 10 cm dilation for a term baby.

The duration of labour varies widely, but active phase averages some 8 hours for women giving birth to their first child ("primiparae") and 4 hours for women who have already given birth ("multiparae").

Second stage: delivery

This stage begins when the cervix is fully dilated, and ends when the baby is finally delivered. It can be very quick, lasting just a few minutes, or take more than two hours. It can be hard work, too, as you're actively pushing the baby out. At the beginning of the normal second stage, the head is fully engaged in the pelvis; the widest diameter of the head has successfully passed through the pelvic brim. Ideally it has successfully also passed below the interspinous diameter. This is the narrowest part of the pelvis. If these have been accomplished, all that will remain is for the fetal head to pass below the pubic arch and out through the introitus. This is assisted by the additional maternal efforts of "bearing down". Pushing might be guided by the midwife who can see whats happening. She might ask you to withhold some pushes, to coordinate them with your breathing, or to breathe through some of the urges. This can help prevent a tear in your perineum, which might happen if the baby comes out too quickly.Your baby's head will emerge first parting the labia, which is known as crowning. At this point the woman may feel a burning or stinging sensation. This is also known as the "ring of fire."

A few more contractions and the head will be born, usually facing towards your back. Your babys shoulders and head will turn sideways. The baby is then fully born. Congratulations!

You can ask to have the baby lifted straight on to you before the cord is cut so that you can feel and be close to each other immediately. Then the cord is clamped and cut, the baby is dried to prevent him or her from becoming cold, and you’ll be able to hold and cuddle your baby properly.

Your baby may be quite messy, with some of your blood and perhaps some of the white, greasy vernix which acts as a protection in the womb still on the skin. If you prefer, you can ask the midwife to wipe your baby and wrap him or her in a blanket before your cuddle.

Sometimes mucus has to be cleared out of a baby’s nose and mouth or oxygen given to get breathing under way. If this happens your baby will be passed to you as soon as possible.

Third stage: placenta

In this stage, the uterus expels the placenta (afterbirth). The placenta is usually delivered within 15-30 minutes of the baby being born. You may not be vary aware of it happening, as most of your attention.  Maternal blood loss is limited by contraction of the uterus following delivery of the placenta. Normal blood loss is less than 600 mL.

As your baby's born, you midwife may ask your consent for you to be given an injection of a synthetic hormone, usually in your thigh or buttock.  It stimulates the uterus to contract, which causes the placenta to come away from the uterus.

The injection contains a drug called Syntometrine or Syntocinon, which makes the womb contract and so helps prevent the heavy bleeding which some women may experience without it.

You may prefer not to have the injection at first, but to wait and see if it is necessary. You should discuss this in advance with your midwife and make a note on your birth plan.

The placenta peels away and the blood vessels on the inside of the uterus close themselves, which stops most of the bleeding (some bleeding is normal).

Some mothers opt for a 'physiological' or natural third stage. This means the uterus contracts by itself, and expels the placenta and membranes. The cord is clamped and then cut when it stops pulsating, after the placenta is delivered.

If this is what you'd prefer to happen, ensure it's in your notes or is part of your birth plan. There are some situations in which it might not be considered safe - if you're at risk of haemorrhage, for instance, or have a problem with blood pressure.

Information sourced from:

https://www.nhs.uk/Planners/pregnancycareplanner/Pages/PregnancyHome.aspx?WT.srch=1

https://en.wikipedia.org/wiki/Childbirth

https://www.bbc.co.uk/parenting/having_a_baby/pregnancy_labour.shtml