MTHFR and male infertility: The results showed enhanced risks of male infertility with the MTHFR 677C>T were acquired both in Azoo (CT+TT vs. CC: fixed effects model, OR = 1.36, 95% CI: 1.18–1.55, P = 0.000, I2 = 49.1%) and OAT (CT+TT vs. CC: fixed effects model, OR = 1.35, 95% CI: 1.11–1.64, P = 0.003, I2 = 44.7%) subgroups.