Separation of the placenta from the wall of the uterus before the baby is delivered
The placenta normally separates from the wall of the uterus after the baby has been born. In placental abruption, part or all of the placenta separates from the uterus before the baby has been delivered. The condition occurs in about 1 in 120 pregnancies and is potentially life-threatening, especially for the fetus. Placental abruption is the most common cause of vaginal bleeding in pregnancy after the 28th week.
There are two basic types of placental abruption: revealed and concealed. A revealed placental abruption causes mild to severe vaginal bleeding. In a concealed placental abruption, there is no visible bleeding from the vagina because blood collects between the placenta and the wall of the uterus.
The exact cause of placental abruption is not known. However, the condition appears to be more common in women who have long-term high blood pressure (see Hypertension). The risk is also increased if a woman smokes during pregnancy, drinks large amounts of alcohol, and/or abuses drugs. The disorder occurs more often after several previous pregnancies or in women who have had a placental abruption in a previous pregnancy. Abdominal injury sometimes leads to placental abruption.
Symptoms usually occur suddenly and depend on how much of the placenta has separated from the wall of the uterus. If only a small part of the placenta has pulled away, bleeding may be minor, but a large separation can cause severe haemorrhage. In increasing order of severity, symptoms may include:
Slight to heavy vaginal bleeding.
Abdominal cramps or backache.
Severe, constant abdominal pain.
Reduced fetal movements.
If you develop vaginal bleeding at any stage of pregnancy, you should consult your doctor or midwife immediately. If the bleeding is heavy, it is advisable to call an ambulance without delay because you may need emergency care.
Your doctor will examine you internally using a speculum, which is an instrument that holds the vagina open. You may also have ultrasound scanning (see Ultrasound scanning in pregnancy), and the fetal heartbeat will be checked. If the separation is small, you may stay in hospital for observation and for monitoring of the fetal heartbeat (see Fetal monitoring).
If bleeding does not stop or restarts, labour may be induced (see Induction of labour). After a large placental abruption, an emergency caesarean section is often needed to save the fetus. You may have a blood transfusion if you lose a lot of blood.
The outlook varies depending on the degree of separation. With appropriate treatment, the mother is not usually in danger. If the condition is minor, the pregnancy often progresses, although the fetus may be at risk of intra-uterine growth retardation. Severe cases may lead to death of the fetus.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.