One study found that those who denied their own pregnancy represented 0.26% of all deliveries.
[1] A later study cited an incidence at 20 weeks gestation of approximately 1 in 475, and said that the proportion of cases persisting until delivery is about 1 in 2500 pregnancies.
Physical symptoms of pregnancy can be absent or not perceived 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 their body.