Mothers' Folate Levels Linked to Birth Weight


Maternal folate status is an important predictor of infant birth weight, a prospective study has shown.

In a cohort of nearly 1,000 expectant mothers, those with lower levels of erythrocyte red blood cell (RBC) folate in early pregnancy were significantly more likely to have low-birth-weight babies, according to Caroline Relton, M.D., and her associates at the University of Newcastle upon Tyne (England).

The researchers investigated the relationship between maternal and newborn RBC folate status, vitamin B12 status, maternal smoking, age, parity, and infant birth rate in 998 pregnant mothers receiving prenatal care at a hospital in northwest England and their newborns. Blood samples were collected from mothers during their first routine prenatal appointment and from the newborns' umbilical cords at birth (Br. J. Nutr. 2005;93:593–9).

In a multivariate analysis, maternal folate status was the only significant determinant of birth weight. Each standard deviation increase in maternal folic acid level was associated with a 14% weight increase in birth weight z score.

Univariate linear regression analysis associated smoking with a significant decrease in birth weight; however, multivariate analysis showed a dramatically reduced, nonsignificant influence, suggesting that smoking and maternal folate status are not independent of each other. Folate levels were significantly lower in women who smoked than in nonsmokers, thus the effect of smoking on birth weight may be mediated in part by its association with maternal folate, according to the authors.

Maternal vitamin B12 status was significantly associated with both maternal and neonatal folate but not with birth weight. However, the relationship between vitamin B12 and maternal folate status suggests this micronutrient has an important role in maternal nutrition during pregnancy, the authors wrote.

Neonatal vitamin B12 had a small but significant influence on infant birth weight when analyzed in a univariate model, but the effect was not significant when considered in a multivariate model, nor was there any association between neonatal folate and birth weight.

Folate is of fundamental importance to cell function, including the synthesis and repair of DNA and gene expression. Although the exact nature of the relationship between folate and birth weight is not known, reductions in folate are associated with increases in the amino acid homocysteine. Elevated homocysteine has been linked to many clinical conditions that affect fetal growth, the authors stated.

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