title: Letter: Neural-tube defects and twinning.
mesh_terms: D000757:Anencephaly / Q000235:genetics*; D002996:Clomiphene / Q000009:adverse effects / Q000494:pharmacology; D004200:Diseases in Twins; D005260:Female; D006720:Homozygote; D006801:Humans; D010060:Ovulation / Q000187:drug effects; D011247:Pregnancy; D011272:Pregnancy, Multiple; D012744:Sex Ratio; D014427:Twins
chemical_list: D002996:Clomiphene