MTHFR and Infertility: Elevated estrogens generate oxidative stress induces placental/obstetrical pathologies.37–39 It is possible to conclude that all these observations should stimulate investigation on the prevalence of c.677C>T MTHFR SNP in infertile patients with endometriosis with increased obstetric risk and subsequently a possible decrease of this risk with 5-MTHF preventive administration, considering the low cost of the drug, its routinary use (in our hands) and prescription in the periconceptional period and its demonstrated harmlessness.