The placenta is a remarkable organ which acts as your baby's life support system, separating her blood stream from yours and providing her with oxygen and nutrients.
The placenta develops during early pregnancy and usually attaches to the top or side of the lining of the womb. Once the placenta is fully developed, at around 12 weeks, it takes over the production of a number of hormones, including oestrogen and progesterone, which control most of the changes that take place in your body during pregnancy.
The umbilical cord, which attaches the baby to the centre of the placenta, carries oxygen and nutrients from your body through the placenta to your baby. Antibodies, which give resistance to infection, pass to the baby in the same way, but so too does alcohol, nicotine and drugs, which is why it is so important to avoid these during pregnancy.
The placenta also filters your baby's waste products into your blood stream so that they can be removed from your body.
Once your baby has been delivered you will be offered an injection to help stimulate your contractions to speed up the delivery of the placenta and membranes; also known as the afterbirth.
You may prefer to allow this third stage of labour to happen naturally; this takes longer and can cause more bleeding. The doctor will check the afterbirth to make sure that nothing has been left behind.
If you have a Caesarean the placenta is delivered after your baby has been lifted from the womb.
Although placental problems are rare, they can occur. These complications include:
Placental praevia - also known as a low-lying placenta, this condition occurs when the placenta is located in the lower part of the womb where it may partially – or completely – cover the cervix, blocking the baby's way out. The position of the placenta will determine the monitoring that you will receive and also whether you will be able to deliver your baby vaginally, or if a Caesarian will be required.
Placental abruption - this is when the placenta starts to peel away from the wall of the womb causing constant pain in the abdomen, contractions and vaginal bleeding.
The severity of the condition depends on how large a portion of the placenta has separated from the womb. If the abruption is minor you may be admitted to hospital until the bleeding stops, if it is severe a Caesarean may be recommended.
Retained placenta - very occasionally the placenta doesn't come away from the lining of the womb during the third stage of labour. Known as a retained placenta, this can lead to severe bleeding so that removal under anaesthetic may be necessary. If some, but not all of the placenta comes away, or if the membranes have been left behind in the womb this can cause heavy blood loss and infection so removal under anaesthetic will be required.
This is known as evacuation of retained products of conception (ERPOC). Once you have a retained placenta it more likely to happen in a subsequent birth so it's important to tell your doctor if you become pregnant again.