Often, the absence of a period (or "amenorrhea") is the first and most common sign of pregnancy. A missed period as a symptom of pregnancy is much more reliable in women who have normal and regular periods.
During pregnancy, a pregnant woman does not ovulate, therefore she will not have periods. In addition to pregnancy, a missed or delayed period can be caused by various reasons not related to pregnancy, just as many other symptoms can be as well including breastfeeding, change in contraceptives, stress, illness and extreme weight loss or being underweight.
Occasionally, women will have light bleeding around the time they would expect their period to come, but it typically doesn't last as long as a normal period and isn't nearly as heavy. If you are pregnant or suspect you're pregnant and experience any bleeding, contact your doctor.
