Perhaps one the earliest signs of pregnancy for women is the cessation of menstrual cycles, or the process through which a woman sheds the inner lining of her uterus.
Menstruation typically stops once a woman becomes pregnant because a fertilized egg -- at this point called a blastocyst -- has implanted itself on to the uterine wall. Keeping these layers allow for the blastocyst to establish itself and develop into a baby.
Occasionally, pregnant women continue to experience periodlike bleeding, which deceives them into thinking they're not pregnant. These false menstrual cycles are rare, and doctors are working to figure out what causes them in some women but not in others.
In other cases, women who don't know they're pregnant until they enter the delivery room may have a history of irregular menstruation cycles; for them, missing a period or randomly experiencing spotting could be the norm. Because of this, pregnant women who believe they're menstruating may still take oral contraceptives to prevent pregnancy.
Read about the role of stress in denied pregnancies on the following page.