The cause of pre-eclampsia is not fully understood. However, it is thought that a problem may develop with the blood vessels in the placenta, causing it to be underdeveloped.
The placenta is the organ that links your blood supply to your unborn baby's blood supply. Food and oxygen is able to pass through the placenta from your blood into the baby, and waste products can pass from the baby back into you.
In order to support your growing baby, the placenta needs a large and constant supply of blood from you. In pre-eclampsia, the placenta does not get enough blood. This could be due to a problem with the placenta that developed as it was forming, during the first half of your pregnancy.
A problem with the placenta
In the initial stages of pregnancy, the fertilised egg implants itself into the wall of the uterus (womb). The uterus is a hollow, pear-shaped organ in a woman where a baby grows during pregnancy. The egg produces root-like outgrowths called villi that help to anchor it to the lining of the uterus.
The villi are fed nutrients through spiral-shaped arteries in the uterus. The villi will eventually grow into the placenta. Some ideas about what causes pre-eclampsia are based on these spiral shaped arteries in the uterus, and the important role they play in the development of the placenta.
During the early stages of pregnancy, these spiral arteries are remodelled (they change shape) and become wider. If the arteries do not fully transform, it is likely that the placenta will not develop properly because it will not get enough nutrients. This may then lead to pre-eclampsia.
The reason why the spiral arteries do not transform as they should is still unclear. Some research has suggested that there might be link between pre-eclampsia, miscarriage, and infertility. It is possible that the same medical reasons that cause infertility and miscarriage, are also responsible for the problems that lead to pre-eclampsia.
However, the exact nature of pre-eclampsia and why it affects certain people, is still being researched.
Disrupted blood flow
The problem with the placenta means that the blood supply between you and your baby is disrupted. Signals from the damaged placenta affect your blood vessels, causing hypertension (high blood pressure). The signals also disturb your kidney function.
Waste products that should be removed from your blood and passed out in your urine, remain in the blood. At the same time, valuable proteins that should remain in your blood are leaked into your urine, causing proteinuria (protein in your urine).
Some factors have been identified that could increase your chance of developing pre-eclampisa. These are listed below.
If it is your first pregnancy, pre-eclampsia it is more likely than during any subsequent pregnancies.
If you have had a child, but it has been at least 10 years since your last pregnancy, your risk of developing pre-eclampsia is slightly higher.
If you have a family history of the condition - for example, if your mother, or any sisters, have had pre-eclampsia, your chances of developing the condition increases.
If you have had pre-eclampsia in a previous pregnancy, there is approximately a 20% chance that you will develop the condition again in later pregnancies.
Your age influences the likelihood of developing pre-eclampsia; if you are a teenager, or over 40 years of age, you have a higher chance of developing it.
If you have an existing medical problem - for example diabetes, kidney disease, migraines, or high blood pressure, you are more at risk of getting pre-eclampsia.
If you are obese at the start of your pregnancy, pre-eclampsia is more likely. Obesity is defined as having a Body Mass Index (BMI) of 30 or more.
If you are expecting multiple babies, such as twins or triplets, pre-eclampsia is more likely because there is more strain on the placenta.
Kidney: Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine.
Genetic: Genetic is a term that refers to genes- the characteristics inherited from a family member.
Blood vessels: Blood vessels are the tubes in which blood travels to and from parts of the body. The three main types of blood vessels are veins, arteries and capillaries.
Blood: Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
High blood pressure: Hypertension is when the pressure of the blood in your bloodstream is regularly above 140/90 mmHG.