Neural tube defects are a heterogenous group of malformations resulting from failure of neural tube closure during early embryogenesis. Anencephaly is the commonest form of neural tube defect and results from failure of closure of the anterior portion of the neural tube. Anencephaly is characterized by absence of the cranium along with cerebral hemispheres that are rudimentary or absent and risk of recurrence after affected child is 2-3%. Periconceptual folic acid intake may decrease the incidence and recurrence of anencephaly.

Most often, anencephaly is discovered by conventional two-dimensional ultrasonography at the time of attempted biparietal diameter determination for fetal age in the second trimester. Two-dimensional transvaginal ultrasonography has a limitation in a motion of the transducer shaft due to narrow space of the vagina. It is sometimes impossible to obtain information of the whole brain and to miss the fetal CNS(central nervous system) anomalies. Recent advanced three-dimensional ultrasonography has remarkably improved not only surface rendering but also multiplanar analysis of internal structure.

Recently, we encountered one case of recurrent anencephaly that had occurred in a same pregnant woman and three-dimensional transvaginal ultrasonography enabled us to diagnose anencephaly at 11³ weeks of gestation. We report this case with brief review of the literatures.