In contrast , we did not find any beneficial effect of  folate supplementation on placental weight or on length of gestation .
There is a paucity of well-conducted RCTs investigating the effect of  folate supplementation on health outcomes in pregnancy .
The beneficial effect of folic acid supplementation before and shortly after conception is well recognized , whereas the effect of supplementation during the second and third trimesters is controversial and poorly documented .
Our aims were to systematic ally review r and omized controlled trials ( RCTs ) investigating the effect of folate supplementation on birth weight , placental weight and length of gestation and to assess the dose – response relationship between folate intake ( folic acid plus dietary folate ) and health outcomes .
A prospective study of micronutrient status in adolescent pregnancy.
BACKGROUND Adolescents are more likely than adults to consume energy-dense , micronutrient-poor diets and to experience adverse pregnancy outcomes . OBJECTIVES The objectives were to assess micronutrient intake  and  blood biomarkers  prospect ively in pregnant adolescents recruited to the About Teenage Eating ( ATE ) Study and to determine associations with pregnancy outcome . DESIGN Pregnant adolescents ( n = 500 ) were recruited from 2 UK inner city population s.  Dietary intake was assessed with three 24-h dietary recalls , and micronutrient status was assessed by measurement of third trimester blood biomarkers . Pregnancy outcomes included small-for-gestational age ( SGA ) birth and preterm delivery . RESULTS Median iron and folate intakes were lower than UK and US recommended amounts . Folate and vitamin B-12 status were lower in smokers , despite no differences in dietary intake . Serum folate was < 7.0 nmol/L in 12 % of subjects , and serum total homocysteine ( tHcy ) was elevated ( > 10 micromol/L ) in 20 % of subjects . Fifty-two percent of the subjects had iron deficiency anemia , and 30 % had serum 25-hydroxyvitamin D concentrations < 25 nmol/L. The incidence of SGA birth was higher in subjects with poorer folate status ( red blood cell folate , P = 0.003 ; serum folate , P = 0.02 ; tHcy , P = 0.01 ; simple regression ) and those with low folate intakes , regardless of the inclusion ( P = 0.021 ) or exclusion ( P = 0.049 ) of intake from supplements ( simple regression ) . Adjustment for confounding variables confirmed the independence of these associations . The risk of SGA birth was also higher in subjects with low food iron intake ( P = 0.049 ) , but not when intake included iron from supplements ( P = 0.21 ) . The risk of SGA birth was lower in subjects with iron deficiency anemia ( P = 0.002 ) . CONCLUSION Poor micronutrient intake and status increase the risk of SGA births in pregnant adolescents
In contrast , we did not find any beneficial effect of  folate supplementation on placental weight or on length of gestation .
There is a paucity of well-conducted RCTs investigating the effect of  folate supplementation on health outcomes in pregnancy .
The beneficial effect of folic acid supplementation before and shortly after conception is well recognized , whereas the effect of supplementation during the second and third trimesters is controversial and poorly documented .
Our aims were to systematic ally review r and omized controlled trials ( RCTs ) investigating the effect of folate supplementation on birth weight , placental weight and length of gestation and to assess the dose – response relationship between folate intake ( folic acid plus dietary folate ) and health outcomes .