Although they're rare, a number of complications can develop if pre-eclampsia isn't diagnosed and monitored.
These problems can affect both the mother and her baby.
Problems affecting the mother
Eclampsia describes a type of convulsion or fit (involuntary contraction of the muscles) that pregnant women can experience, usually from week 20 of the pregnancy or immediately after the birth.
Eclampsia is quite rare in the UK, with an estimated 1 case for every 4,000 pregnancies.
During an eclamptic fit, the mother's arms, legs, neck or jaw will twitch involuntarily in repetitive, jerky movements.
She may lose consciousness and may wet herself. The fits usually last less than a minute.
While most women make a full recovery after having eclampsia, there's a small risk of permanent disability or brain damage if the fits are severe.
Of those who have eclampsia, around 1 in 50 will die from the condition. Unborn babies can suffocate during a seizure and 1 in 14 may die.
Research has found that a medication called magnesium sulfate can halve the risk of eclampsia and reduce the risk of the mother dying.
It's now widely used to treat eclampsia after it's occurred and treat women who may be at risk of developing it.
HELLP syndrome is a rare liver and blood clotting disorder that can affect pregnant women.
It's most likely to occur immediately after the baby is delivered, but can appear any time after 20 weeks of pregnancy, and in rare cases before 20 weeks.
The letters in the name HELLP stand for each part of the condition:
- "H" is for haemolysis – this is where the red blood cells in the blood break down
- "EL" is for elevated liver enzymes (proteins) – a high number of enzymes in the liver is a sign of liver damage
- "LP" is for low platelet count – platelets are substances in the blood that help it clot
HELLP syndrome is potentially as dangerous as eclampsia, and is slightly more common.
The only way to treat the condition is to deliver the baby as soon as possible.
Once the mother is in hospital and receiving treatment, it's possible for her to make a full recovery.
The blood supply to the brain can be disturbed as a result of high blood pressure. This is known as a cerebral haemorrhage, or stroke.
If the brain doesn't get enough oxygen and nutrients from the blood, brain cells will start to die, causing brain damage and possibly death.
- pulmonary oedema – where fluid builds up in and around the lungs. This stops the lungs working properly by preventing them absorbing oxygen.
- kidney failure – when the kidneys can't filter waste products from the blood. This causes toxins and fluids to build up in the body.
- liver failure – disruption to the functions of the liver. The liver has many functions, including digesting proteins and fats, producing bile and removing toxins. Any damage that disrupts these functions could be fatal.
Blood clotting disorder
The mother's blood clotting system can break down. This is known medically as disseminated intravascular coagulation.
This can either result in too much bleeding because there aren't enough proteins in the blood to make it clot, or blood clots developing throughout the body because the proteins that control blood clotting become abnormally active.
These blood clots can reduce or block blood flow through the blood vessels and possibly damage the organs.
Problems affecting the baby
Babies of some women with pre-eclampsia may grow more slowly in the womb than normal.
This is because the condition reduces the amount of nutrients and oxygen passed from the mother to her baby.
These babies are often smaller than usual, particularly if the pre-eclampsia occurs before 37 weeks.
If pre-eclampsia is severe, a baby may need to be delivered before they're fully developed.
This can lead to serious complications, such as breathing difficulties caused by the lungs not being fully developed (neonatal respiratory distress syndrome).
In these cases, a baby usually needs to stay in a neonatal intensive care unit so they can be monitored and treated.
Some babies of women with pre-eclampsia can even die in the womb and be stillborn.
It's estimated around 1,000 babies die each year because of pre-eclampsia. Most of these babies die because of complications related to early delivery.