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. This evidence concerns the gene MTHFR and endometriosis.