MTHFR and isolated spina bifida: The MTHFR 677C > T polymorphism, one of the most prevalent single-nucleotide polymorphisms (SNPs) of the MTHFR gene, has also been identified as a risk factor for various adverse pregnancy outcomes, such as fetal aneuploidy [5], congenital heart defects (CHDs) [6], neural tube defects (NTDs) [7, 8], cleft lip and palate (CLP) [4, 9], and recurrent embryo loss [10].