Few Side Effects
Women who don't know they're pregnant until they rush to the delivery room rarely recall hard-hitting side effects like fatigue, nausea (also known as "morning sickness"), tender breasts, headaches, food cravings, back pain, soreness and weight gain.
Since the raging hormones related to pregnancy affect different women in different ways, it's not surprising that some experience different pains and sensations. Women who don't know they're pregnant until they're in labor may confuse the side effects of pregnancy with other problems, including stress, food poisoning or indigestion.
Next, let's look at whether menstrual cycles influence whether a woman knows she's with child.