den Dekker HT, et al. - This study was designed to explore the associations of maternal folic acid supplement use and folate, vitamin B₁₂ and homocysteine concentrations during pregnancy with childhood lung function and asthma. Findings demonstrated that based on methylenetetrahydrofolate-reductase polymorphism C677T (MTHFR-C677T) carriership, childhood lung function might be adversely influenced by preconceptional start of maternal folic acid supplement use and higher vitamin B₁₂ concentrations at birth.