What causes Anencephaly?

Anencephaly, along with all other Neural Tube Defects (NTDs) are caused by not just one factor. Each case is different. It is due to a combination of factors which are environmental, genetically and physiological.
What we, as people who have first hand experience of Anencephaly, want to reassure you is that it is something caused by nature and nothing that the mother has done wrong. Mothers grieve for their children in different ways but a common stage is anger of themselves and hatred of their bodies. There is (and was) nothing you could've done to prevent your Anencephaly Angel!