Mom’s folate levels tied to baby’s birthweight

Higher maternal folate levels translate to greater offspring birthweight, a study has found.

The results were based on a two-sample Mendelian randomization (MR). The first sample was obtained from a genome-wide association study of 45,576 individuals. The second sample was from the latest Early Growth Genetics consortium meta-analysis with 297,356 individuals reporting their own birthweight and 210,248 women reporting their offspring's birthweight.

There was no evidence for a causal effect of maternal B12 levels on offspring birthweight (0.009 standard deviation [SD] change in birthweight per 1 SD higher B12; p=0.469) or of foetal B12 levels on their own birthweight (−0.012 SD change in birthweight per 1 SD higher B12; p=0.478). Results were regardless of the method of analysis used. 

On the other hand, maternal folate levels showed a positive causal effect on offspring birthweight (71-g increase per 1 SD higher folate). There was some evidence for a small inverse effect of foetal folate levels on their own birthweight (25-g reduction per 1 SD higher folate).

The present data are in line with evidence from randomized controlled trials reporting that higher maternal folate levels contribute to an increase in offspring birthweight.

On the other hand, the absence of a causal effect of B12 levels on offspring birthweight suggests that previous observational studies may have been confounded. However, this does not mean that B12 levels do not influence the development of the foetus. Rather, B12 levels could promote growth in a particular period of the pregnancy, affecting a particular organ or growth of fat, lean, or skeletal tissue in different directions, which may not be shown in an outcome such as birthweight.