Denial of pregnancy (also called pregnancy denial) is a rare form of denial exhibited by women to either the fact or the implications of their own pregnancy. One study found that women who denied their pregnancy represented 0.26% of all deliveries. A later study cited that at 20 weeks gestation approximately 1 in 475 pregnant women denied their pregnancy, and said the proportion of cases persisting even until delivery is about 1 in 2500 refusing to acknowledge that they are pregnant.
Denial of pregnancy Wikipedia
This is a form of denial that is so extreme as to fall under the category of delusion. While physical symptoms of pregnancy do usually occur they are sometimes misinterpreted by the woman. Some women interpret the sensation of something growing inside them as cancer, or a blood clot. Some women might believe fetal movements are their organs coming loose inside her body. During the psychotic denial pregnancy women tend to hide their pregnancy from everyone and put their fetus at a high risk.