Background:　Myo-inositol　(MI)　deficiency　is　associated　with　an　increased　risk　for　neural　tube　defects　(NTDs),　mental　disorders　and　metabolic　diseases.　We　developed　a　gas　chromatography-mass　spectrometry　(GC-MS)　method　to　detect　MI　in　human　plasma,　which　was　accurate,　relatively　efficient　and　convenient　for　clinical　application.　Methods:　An　external　standard　method　was　used　for　determination　of　plasma　MI.　Samples　were　analyzed　by　GC　MS　after　derivatization.　The　stable-isotope　labeled　internal　standard　approach　was　used　to　validate　the　method＇s　accuracy.　Alpha　fetal　protein　(AFP)　was　detected　by　chemiluminescence　immunoassay.　Results:　The　method　was　validated　by　determining　the　linearity,　sensitivity　and　recovery　rate.　There　was　a　good　agreement　between　the　internal　standard　approach　and　the　present　method.　The　NTD-affected　pregnancies　showed　lower　plasma　MI　(P　=　0.024)　and　higher　AFP　levels　(P　=　0.001)　than　control.　Maternal　MI　level　showed　a　better　discrimination　in　spina　bifida　subgroup,　while　AFP　level　showed　a　better　discrimination　in　anencephaly　subgroup　after　stratification　analysis.　Conclusions:　We　developed　a　sensitive　and　reliable　method　for　the　detection　of　clinical　plasma　MI,　which　might　be　a　marker　for　NTDs　screening,　and　established　fundamental　knowledge　for　clinical　diagnosis　and　prevention　for　the　diseases　related　to　disturbed　MI　metabolism.　(C)　2016　Elsevier　B.V.　All　rights　reserved.