Are PMS Symptoms a Sign of Pregnancy?

Symptoms of PMS and signs of pregnancy can be identical. PMS remains a medical enigma, since symptoms vary from woman to woman. Women begin to build progesterone in the body near ovulation, in anticipation of pregnancy, at about the same time that PMS occurs (about 10 days before menses). When an egg isn't fertilized, progesterone levels drop, PMS disappears and menses begins. If the egg is fertilized, progesterone levels continue to rise to help the body support pregnancy.

Are you pregnant or just PMSing?
Because the following conditions are all caused by a surge of progesterone to prepare the body for pregnancy, it is hard to distinguish at an early stage whether pregnancy has occurred or whether it's just the end of an ovulation cycle. When a woman is trying to get pregnant, this can be especially frustrating. The difference between symptoms of PMS and signs of pregnancy is that symptoms of PMS are short-lived. They last a few days to a week, depending on each woman's individual reaction to progesterone. When progesterone levels fall, the symptoms vanish. During pregnancy, progesterone levels stay elevated and the related nausea, cravings, breast tenderness and other pregnancy indicators often are more severe and last much longer--usually 12 or more weeks.

Fatigue
Fatigue as a symptom of PMS lasts a few days, but can last for the entire first trimester for some pregnant women.

Nausea
It's not just pregnant women who get sick; nausea also can be a part of PMS that, fortunately, usually lasts just a day or two.

Moodiness
Hormones can be responsible for moodiness both before menstruation and during pregnancy.

Hunger
Craving certain foods while "PMS-ing" is just as common as pregnancy cravings.

Breast tenderness
Women often experience breast tenderness before their period and throughout pregnancy.

source : http://www.ehow.com/facts_5114201_pms-symptoms-sign-pregnancy.html