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Third stage of labour
 
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The third stage

During the third stage of labour the placenta becomes detached from the wall of your uterus and is delivered down the birth canal.

The third stage
© Jupiter

The large blood vessels running to and from the placenta, which are about the thickness of a pencil, are simply torn across. Despite this, bleeding is rare because the muscle fibres of the uterus are arranged in a criss-cross fashion so that when the uterus contracts down, the muscles tighten around the blood vessels and prevent them from bleeding. This is why it's absolutely essential that your uterus contracts down into a hard ball once the placenta has been expelled. Massaging every now and then for an hour or so after the third stage is complete can help keep your uterus tightly contracted. Normally the third stage lasts about ten to 20 minutes but with active management it can be much shorter.

The third stage placenta delivery

Usually your midwife won't try to deliver the placenta until there are clear signs that it's separating from the wall of your uterus and moving down into your vagina. The signs your attendants will look out for are contractions starting up again a few minutes after the birth of your baby, which shows that the placenta is about to separate, and your desire to bear down - this also shows that the placenta has separated from the wall of your uterus and is pressing down on your pelvic floor.

Once these signs have appeared, your midwife may encourage the delivery of the placenta by pulling gently on the cord, at the same time pressing above the rim of the pelvis to control descent. The placenta is expelled from your vagina, followed by the membranes. Rarely, a blood clot will also be expelled.

Delivery

The placenta may pass through your vulva in two different ways. In the first, the centre of the placenta comes out first, dragging the membranes behind it. In the second, an edge of the placenta presents first, then it slips out of the vulva sideways. Most women want to see the placenta - it's an amazing organ that's been the life-support system for your baby for nine months.

After delivery

Once the placenta is delivered, the midwifery staff will check it carefully to make sure it's complete and none of it has been left behind. If any of the placenta has been left in the uterus it can cause haemorrhaging later on, so must be removed as soon as possible. If there's any doubt, you may have a small procedure (ERPC) to ensure the uterus is completely empty. The membranes should form a complete bag except for the hole through which your baby has passed. Your midwife will also check the cut end of the cord to make sure that the umbilical blood vessels are normal. After the placenta is delivered, the whole of your vulval outlet will be examined carefully for tears. Anything other than a minute one will be stitched immediately.

Active management of the third stage

Since the use of ergometrine began in 1935, the third stage of labour has been more actively managed by doctors and midwives. Giving ergometrine at the time of birth was soon found to reduce the number of cases of excessive bleeding, defined as loss of more than 500ml (18floz) of blood (postpartum haemorrhage).

Ergometrine causes the prolonged contraction of the uterus without a period of relaxation - while the uterus is contracted there's not likely to be any bleeding. The placenta separates very quickly from the uterine wall once the uterus starts to contract, so shortening the third stage.

Syntometrine

Most midwives now use a combination of ergometrine and syntocinon known as syntometrine. Ergometrine on its own is rather slow to start to work and can cause nausea, but using it with syntocinon, which acts quickly to stimulate uterine contractions, gives a better result.

Syntometrine is given by injection just as your baby's head is crowning, or when her first shoulder is delivered. It's used automatically in most hospital births to reduce the risk of postpartum haemorrhage. The hormone oxytocin is naturally produced by your body when you see and touch your baby and put her to your breast. It does the same job as syntometrine, but is less reliable.

How you'll feel during the third stage

You may find yourself shivering with cold after the placenta's delivered. My own explanation of this is that your body has suddenly been deprived of the baby's heat inside you and your temperature drops. The only way the body can raise its temperature is to generate heat through muscular work and that's what shivering does - rapid contraction and relaxation of muscles produces body heat. The shivering usually passes in about half an hour, by which time your body temperature is back up to normal.

The placenta

Most first-time mothers are keen to have a look at their placenta.

The placenta measures about 20-25cm (8-10in) in diameter and weighs about 450g (1lb). It's shaped like a disc and its two surfaces look very different from each other.

The baby's side was adjoining the wall of your uterus and covered with membranes. It's flat and smooth, with blood vessels radiating out from the umbilical cord. Your side of the placenta was embedded in the wall of your uterus, and is made up of wedges (cotyledons) to make a larger surface area for the exchange of gases. This side of the placenta is dark red and looks like several pieces of raw liver joined together.

Postpartum haemorrhage

This is rare, largely because your uterus has a self-protecting device to stop it from bleeding.

Once your uterus is completely empty, it contracts down to about the size of a tennis ball. The contraction of the uterine muscles nips the uterine arteries so that they can't bleed. Under normal circumstances there's little bleeding after the delivery. What little bleeding there is appears as the lochia - the usual vaginal discharge after delivery. The lochia is red for two to three days, then turns brown, and disappears within two to six weeks.

If part of the placenta is retained in the uterus it may bleed and this bleeding is called postpartum haemorrhage. This is why the placenta is checked so if any part is missing it can be removed. If this is necessary, the mother is given a general or regional anaesthetic and any remaining placental tissue is gently taken out.

If there's any bleeding more than 24 hours after delivery, your lochia may become bright red again. This can happen if you're too energetic. Check with your doctor, who'll probably suggest that you rest for several days. If the bleeding starts again or becomes heavy, it can be the sign of infection or that a small piece of placenta has been retained. Call your doctor at once. If you pass large clots of blood, call an ambulance to take you to the nearest maternity unit.

Posted 16.11.2010

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