<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by anencephaly ? [/INST] Anencephaly is one of the most common types of neural tube defect, affecting about 1 in 1,000 pregnancies. However, most of these pregnancies end in miscarriage, so the prevalence of this condition in newborns is much lower. An estimated 1 in 10,000 infants in the United States is born with anencephaly. </s>