Normally, the placenta remains firmly attached to the wall of the womb until after the baby has been born. In a small number of cases (about 1 per cent), though, it separates before the baby is born. This is sometimes known as 'accidental bleeding' or 'accidental haemorrhage' or 'placental abruption'.

It is described as 'accidental' because what causes it is unknown, although it may be associated with high blood pressure or with the mother being poorly nourished. It may also be connected with smoking or taking recreational drugs. Occasionally it can happen as the result of an accident, such as a fall.

The amount of separation can vary between a small amount of the placenta coming away and it detaching completely. It can happen at any time from mid-pregnancy onwards.

•   What are the signs?
•   Will it harm by baby?
•   What can be done about it?

In most cases, there's heavy bleeding from the vagina, although this doesn't always happen as the bleeding may be contained behind the placenta. There's often pain in the lower abdomen as well, and sometimes some cramping. You may show signs of shock - feeling weak and dizzy, having a rapid pulse, and looking very pale.

It depends on how much of the placenta has come away. If it's only a small amount, your baby will probably be alright. With more extensive separation, it's likely that the baby will become distressed. If more than half the placenta comes away, the baby may die.

If you have any bleeding at any time, especially if you also have pain in your abdomen, or if you have continuous pain without any bleeding, phone your doctor immediately, or go straight to hospital, so that you can be examined.

If the bleeding is only slight, and the baby's heart rate is normal, you will probably be advised to stay in hospital to rest for a few days until the bleeding stops. You may be offered an ultrasound scan to check whether the placenta has separated or is low-lying.

If the bleeding is severe, and there are signs that the baby is distressed, it will probably be necessary for the baby to be delivered, usually by Caesarean. This is so that the bleeding can be controlled and the risks to the baby can be reduced.