Well, sometimes the body doesn't show the typical signs. Some women are so busy with their daily lives, like working long hours or taking care of a big family, that they overlook the small changes. Maybe there's a bit of fatigue, but they assume it's because they're overworked. And the baby might be positioned in a way that doesn't cause much obvious abdominal growth, especially in the early months.
One reason could be that the woman is overweight. Extra weight can sometimes mask the physical changes of pregnancy. Also, some medical conditions can interfere with the normal hormonal signals that would typically make a woman aware of pregnancy. For instance, certain thyroid disorders. In addition, if a woman has a history of not being very in - tune with her body's normal functions, she might not notice the more subtle signs of pregnancy like breast tenderness or a very slight increase in body temperature.