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According to the researchers, led by Dr Shi Wu Wen at the University of Ottawa, adequate levels of folate may play an important role in the development of the placenta. Folate appears to have a beneficial effect on endothelial cells, special cells that line blood vessels throughout the body and in the placenta.
Pre-eclampsia, also called toxaemia of pregnancy, is a rapidly progressive disorder characterised by protein in the urine and high blood pressure. This may be followed by swelling and sudden weight gain, as well as headaches and changes in vision. However, some women may experience progression of the condition with few symptoms.
Affecting at least five to eight percent of all pregnancies, pre-eclampsia and other blood pressure disorders of pregnancy are a leading global cause of maternal and infant illness and death.
Large doses of folic acid may help
Pre-eclampsia may progress to eclampsia, a more serious condition in which seizures begin to occur. Complications of eclampsia include separation of the placenta and premature delivery.
Preeclampsia is currently believed to be a two-stage disorder, Wen said. During stage I, which probably begins in the late first trimester or early second trimester, there is a decrease in blood flow in the placenta. During stage II, which probably begins in the early third trimester, the syndrome of pre-eclampsia develops, caused by abnormalities of the mother's endothelial cells. Impaired blood vessel formation, inflammation, and nervous system abnormalities may all be contributing factors, the researcher explained.
They hypothesised that large doses of folic acid in early pregnancy may work at both stages of pre-eclampsia.
How the study was done
Wen and colleagues followed nearly 3 000 pregnant women who were seen for prenatal care between week 12 and week 20 of pregnancy. Their findings appear in the American Journal of Obstetrics and Gynaecology.
A total of 2 713 (92 percent) women were taking folic acid alone or multivitamins that contained folic acid, usually at doses of 1.0 milligrams or higher.
As the researchers suspected, folic acid supplements led to a lower rate of pre-eclampsia. Pre-eclampsia developed in 2.17 percent of women taking folic acid and in 5.04 percent of those not taking supplements.
After the researchers adjusted the data to take into consideration the influence of maternal age, ethnicity, education level, number of previous pregnancies, body weight, income, smoking, high blood pressure, diabetes and history of pre-eclampsia, Wen's group found that folic acid reduced the risk of pre-eclampsia by about two thirds.
Folic acid vital early in pregnancy
Whether the women started folic acid supplements - before or after conception - or whether the women discontinued or continued folic acid in the third trimester, "the rate of pre-eclampsia was lower than in those women who did not have supplementation," Wen's team reports.
The doctors conclude that "for pre-eclampsia prevention, folic acid supplementation in the late first trimester or early second trimester, the most critical time window for pre-eclampsia development, may be the most important."
Current guidelines recommend 4mg or 5mg of folic acid for women who have high-risk pregnancies or are at risk for neural tube defects, such as spina bifida, Wen said.
Very high doses of folic acid, however, can cause stomach problems, skin disorders and seizures.
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