Chemicals in fat tissue may trigger pre-eclampsia in some pregnant women, a study suggests.
Pre-eclampsia is a serious condition
Researchers in the United States studied over 1,000 pregnant women. About 6% went on to develop pre-eclampsia.
The condition causes a woman's blood pressure to rise sharply, putting both mother and baby at risk.
The researchers found a direct link between the women's weight before they became pregnant and their risks of developing pre-eclampsia.
For instance, women who were obese before they were pregnant were three times more likely to develop pre-eclampsia compared to those of normal weight.
Women who were overweight were twice as likely to suffer problems. Those who were underweight were half as likely to experience difficulties compared to those of normal weight.
In fact, the risks increased steadily depending on how much body fat the women had before they were pregnant.
The researchers, who are based at the Magee Women's Research Institute in Pittsburgh, said this suggested that body fat played a role in determining who was at risk.
While further studies are needed, they suggested that chemicals produced by fat tissue may be responsible.
Speaking at the American Society for Nutritional Sciences annual meeting in Washington, they said the findings could lead to new treatments to protect against the condition.
However, they said the findings also highlighted the importance for women of being normal weight when they become pregnant.
Researchers at the University of Glasgow were recently awarded almost £129,000 by the British Heart Foundation to carry out research in this area.
They will compare blood plasma from women who have had pre-eclampsia with plasma taken from healthy pregnant women.
They believe that in some women plasma can stimulate fat cells and cause them to release excessive amounts of fatty acids and other toxic products triggering pre-eclampsia.
Mike Rich, chief executive of Action on Pre-Eclampsia, said women planning to become pregnant can take action to reduce their risks of developing the condition.
"The Magee research confirms what we have known about increased BMI being linked to a greater risk of pre-eclampsia.
"However, it goes further and shows that even small increases in BMI can be significant.
"There is a clear health message. We would advise all women, pregnant and considering becoming pregnant to eat a sensible and healthy diet in order to help reduce the risk of pregnancy complications such as pre-eclampsia.
"Women should also ensure that they attend all of their antenatal appointments for blood pressure monitoring and urine testing."