Fetus deformities are caused by both genetic and nongenetic factors. In some cases, the reasons could be anticipated by the family quite early. But the medical community has discovered that in most cases there is no forewarning. Many mothers take no medications or X-rays during pregnancy, nor do they have any particular health problems.
胎兒畸型有遺傳與非遺傳因素，部分原因可以由家族病例早期預知，但醫學界發現，多數畸型胎兒幾乎無警兆﹘﹘許多母親在懷孕時並未服藥、照 X 光，身體也查不出特殊疾病。