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 .
Occurrence of omphalocele in relation to maternal multivitamin use: a population-based study.
OBJECTIVE We evaluated the association between mothers ' use of multivitamin supplements and their infants ' risk for omphalocele , a congenital anomaly of the abdominal wall . Omphalocele can occur in certain multiple congenital anomaly patterns with neural tube defects , for which a protective effect of multivitamins with folic acid has been demonstrated . METHODS We used data from a population -based case-control study of infants born from 1968 - 1980 to mothers residing in metropolitan Atlanta . Case-infants with nonsyndromic omphalocele ( n = 72 ) were actively ascertained from multiple sources . Control-infants ( n = 3029 ) , without birth defects , were selected from birth certificates by stratified r and om sampling . RESULTS Compared with no use in the periconceptional period , periconceptional use of multivitamin supplements ( regular use from 3 months before pregnancy through the first trimester of pregnancy ) was associated with an odds ratio for nonsyndromic omphalocele of 0.4 ( 95 % confidence interval [ CI ] : 0.2 - 1.0 ) . For the subset comprising omphalocele alone or with selected midline defects ( neural tube defects , hypospadias , and bladder/cloacal exstrophy ) , the odds ratio was 0.3 ( 95 % CI : 0.1 - 0.9 ) . These estimates were similar when the reference group also included women who began using multivitamins late in pregnancy ( during the second or third month of pregnancy ) . The small number of participants limited the precision of subgroup analyses and translated into wide confidence intervals that included unity . CONCLUSIONS Periconceptional multivitamin use was associated with a 60 % reduction in the risk for nonsyndromic omphalocele . These findings await replication from additional studies to confirm the findings , generate more precise estimates , and detail possible mechanisms of actions
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 .