After reviewing more than a dozen well designed studies that looked at the relationship between vitamin and/or mineral supplementation and birth outcomes, researchers from Canada have concluded that prenatal multimicronutrient supplementation is associated with a significantly reduced risk of low birth weight and with improved birth weight when compared with iron–folic acid supplementation.

 
Led by Dr. Prakesh Shah from the University of Toronto, the researchers looked at data from 13 studies published between 1998 and 2008 -- all of which looked at the relationship between vitamin and/or mineral supplemenation and birth outcomes including completed weeks gestation, birth weight, preterm birth (birth before 37 weeks of gestation), small-for-gestational-age birth (birth weight too low for gestational age, also known as intrauterine growth retardation), and having a low birth weight (birth weight less than 2500 grams). Included were only those studies that compared outcomes among groups of pregnant women taking supplements versus those taking a placebo and/or iron–folic acid supplementation.

Compared to women receiving a placebo, the researchers noted a significantly reduced risk of having a child born with a low birth weight among women regularly taking a multivitamin/mineral supplement. Similarly, infants born to women taking a supplement tended to be heavier than infants born to women taking a placebo or iron-folic acid supplementation. No significant differences in the risk of preterm birth or small-for-gestational-age was observed.

Although the researchers pointed to a need for more research on the topic, they suggested that prenatal providers world-wide need to "ensure that pregnant women receive multimicronutrient supplementation during the prenatal period." The suggest that the "current strategy recommended by the World Health Organization of providing only iron–folic acid supplementation to pregnant women [should be] challenged in light of the evidence from [this] review."  The review was published by the Journal of the Canadian Medical Association.