This is a truly frightening condition that can develop in pregnancy which can be fatal for mother and baby. If it is suspected, immediate action needs to be taken.

It can affect kidneys, liver, brain and the placenta. It can also harm the unborn baby.
As well as pre-eclampsia, there are two other main reasons why a woman might have high blood pressure in pregnancy. Firstly, her blood pressure may have been high when she became pregnant - sometimes long-standing high blood pressure (chronic hypertension) is diagnosed for the first time during the routine check-ups done when a woman is pregnant. With chronic hypertension the risk of developing pre-eclampsia is increased.

It is worth knowing that the other type of high blood pressure during pregnancy is known as pregnancy-induced hypertension (PIH). This is not generally as serious. This is when high blood pressure develops after 20 weeks of pregnancy, but you don't have the other signs of pre-eclampsia and your blood pressure returns to normal soon after delivery. Half of women who have PIH before 32 weeks of pregnancy go on to develop pre-eclampsia.

During normal pregnancy, your blood pressure tends to fall during the first and second trimesters (up until 24 weeks of pregnancy). With pre-eclampsia, high blood pressure develops after around the 20th week of pregnancy, and stays high until the baby is born. If you develop mild pre-eclampsia, you won't have any symptoms - and it's often first found when your blood pressure and urine are checked during a routine antenatal visit.

If preeclampsia is more advanced, the following symptoms are likely:
severe and persistent headache
vision problems such as flashing lights, blurred vision, stripes, 'floaters' or blackouts
severe pain just below your ribs, especially on the right side
swelling, of your face, hands or feet that develops suddenly
vomiting or feeling sick
These symptoms aren't always due to pre-eclampsia, but if you have any of them it's important to talk to your midwife or GP.

Pre-eclampsia doesn't just affect blood pressure - if it's severe it can lead to stroke, kidney failure and liver problems.
It's known as pre-eclampsia because if left untreated it can result in eclampsia. This is a seizure (fit). Eclampsia can happen at any time during the second half of pregnancy, during labour or after delivery. Almost half of women who develop eclampsia develop it after the baby is born, usually within 24 hours of delivery.
Eclampsia only affects around two in 100 women with pre-eclampsia, because pre-eclampsia can be treated once it's been diagnosed.

What actually happens with pre-eclampsia, is that there are problems with the placenta (the organ that supplies blood and nutrients to the developing foetus ), which, together with high blood pressure can reduce the blood flow to the growing baby. This means that he or she may not receive enough oxygen and nutrients. This can slow a baby's growth, a condition called intra-uterine growth restriction (IUGR). This is sometimes picked up during a routine antenatal appointment, if a midwife or GP finds that the uterus (womb) measures smaller than expected for the stage of pregnancy.
If the oxygen supply to the baby continues to be reduced, he or she may need to be delivered early or even immediately. If this happens before 37 weeks' the baby will be premature. Premature babies are at risk of complications because many of their organs (especially the heart and lungs) may not be ready to work outside the womb. The earlier a baby is delivered, the greater the risk of serious medical complications. However, this needs to be balanced against the risks of your baby not receiving enough oxygen if he or she is not delivered early.

Doctors don't know the exact cause of pre-eclampsia. However, it seems to start with a problem with the placenta. In pre-eclampsia the placenta has not properly developed and its blood supply is reduced.

Doctors don't know why some women get pre-eclampsia and others don't, but there are certain factors that put you at a higher risk. Your family history is important - if your mother had pre-eclampsia, there is a two in 10 chance that you will develop pre-eclampsia during pregnancy too.

You're also more likely to get pre-eclampsia if this is a first baby, you had pre-eclampsia in an earlier pregnancy, you have had a long interval (more than 10 years) between pregnancies, you're having twins or other multiple pregnancies
, you're over 40, you have other medical conditions including high blood pressure, diabetes, kidney disease and antiphospholipid syndrome, you're obese, ie you have a BMI (body mass index) of over 35