MONTEREY, CALIF. — Ingestion of flax oil by women during the second and third trimester of pregnancy is associated with almost a threefold increase in the rate of premature birth, according to the findings of a recent study.
The format of the study questionnaire did not allow investigators to estimate the dose of flax oil associated with preterm birth, study investigator Anick Bérard, Ph.D., of the University of Montreal said in an interview.
Dr. Bérard noted that the question about flax referred specifically to flax oil, which is often used for constipation during pregnancy, and not flax seed, a common foodstuff.
The investigators found no link between premature birth and ingestion of a number of other herbal products, including chamomile, peppermint, and green tea, wrote lead author Krystel Moussally, B.Sc., of the University of Montreal, and her colleagues in a poster presentation at the annual meeting of the Teratology Society.
The case-control study involved 3,354 women listed in the Quebec Pregnancy Registry who responded to a questionnaire. All gave birth to a live infant between 1998 and 2003 in Quebec hospitals and all were continuously insured by the Regie de l'assurance maladie du Québec drug plan for at least 12 months before and during pregnancy. In all, the investigators mailed 8,505 questionnaires, so the response rate was 39%.
Among the women who returned questionnaires, 22% had given birth before 37 weeks' gestation.
As expected, women who gave birth prematurely differed from the controls on a number of variables.
For example, they were more likely to have asthma, and they had fewer prenatal visits.
After controlling for health status, sociodemographic characteristics, lifestyle habits, medication use before and during pregnancy, pregnancy complications, and the baby's sex, the investigators found that women who used flax oil during their last two trimesters were 2.76 times more likely to give birth prematurely than were those who did not.
“Flax use should be avoided during pregnancy,” the investigators concluded. “Caution in the use of not-as-yet regulated [herbal products] during the last two trimesters of pregnancy is warranted.”
The investigators stated that they had no conflicts of interest to declare.