Results: The fetal, but not maternal, MTHFR rs1801133 genotype was associated with ELBW (OR = 1.65; 95% CI: 1.09–2.51; p = 0.017, dominant model), bronchopulmonary dysplasia (p = 0.028), patent ductus arteriosus (p = 0.017), and neonatal mortality. This evidence concerns the gene MTHFR and Patent ductus arteriosus.