Large study links folic acid supplementation with reduced risk of preeclampsia during pregnancy

January 4, 2008

Folic acid supplementation during pregnancy has long been known to reduce the risk of birth defects in newborns, but a new study now suggests that the vitamin may also reduce the risk of preeclampsia, a leading cause of maternal and infant illness and death worldwide.

As described in the January 2008 issue of the American Journal of Obstetrics and Gynecology, researchers closely followed approximately 3,000 pregnant women at The Ottawa Hospital and the Kingston General Hospital and found that preeclampsia occurred in 2.2 per cent of women who took multivitamins containing folic acid compared to 5.1 per cent of women who did not. The study was purely observational and women were not asked to make any changes to their daily lifestyle or health care. Known preeclampsia risk factors such as maternal age, education level and previous preeclampsia were controlled for and the difference was found to be significant by conventional standards.

Because of the known association of folic acid and reduced risk of birth defects, Health Canada currently recommends that all pregnant women take 0.4 mg folic acid per day while the Society of Obstetricians and Gynaecologists of Canada recommends a dose of 1 mg per day. In the current study, 92 per cent of women were taking folic acid, mostly at the higher dose.

Preeclampsia is characterized by high maternal blood pressure and urine protein – conditions that increase the risk of stroke, kidney problems, premature birth and other complications. There are currently no established treatments to prevent preeclampsia or lessen its effects.

“Previous smaller observational studies had suggested a link between folic acid and reduced risk of preeclampsia, but our study is the largest yet to test this association, and it was very carefully designed,” said lead author Dr. Shi Wu Wen, a Senior Scientist at the Ottawa Hospital Research Institute and Professor at the University of Ottawa. “The data also makes sense from a biological standpoint, because we know that folic acid has an important role in the development and function of blood vessels, and increasing evidence suggests that this process is disrupted in women with preeclampsia.”

The researchers have applied for funding to conduct a randomized controlled trial to determine if there is a cause-and-effect relationship between folic acid dose and risk of preeclampsia. Because the current study was observational in nature, it could only reveal associations.

“Eventually, this research could help us significantly reduce pregnancy complications, but for now, women should continue to follow the current folic acid guidelines,” said Dr. Mark Walker, coauthor of the study and a high-risk obstetrician at The Ottawa Hospital.

This study was funded by the Canadian Institutes for Health Research. The full publication is available here.

About the Ottawa Hospital Research Institute
The Ottawa Hospital Research Institute (OHRI) is the research arm of The Ottawa Hospital and an affiliated institute of the University of Ottawa. The OHRI includes more than 1,300 scientists, clinical investigators, graduate students, postdoctoral fellows, and staff conducting research to improve the understanding, prevention, diagnosis and treatment of human disease. For more information, visit

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