The First Trimester
(Week 1 - Week 12)
Your period stops or becomes very light.
You may feel nausea or queasiness. Some women vomit. ("Morning sickness" can happen any time of day -- it may help to eat small meals throughout the day, snack on crackers or toast, or drink juice or lemonade.)
Your breasts swell and may be tender.
Your nipples and the area around the nipples (areola) get darker and broader.
You have to urinate more often.
You feel tired.
You may become constipated and have heartburn (Tums may help).
You may have headaches.
You experience mood swings -- feel angry, sad, or happy for no reason.
The Second Trimester
(Week 13 - Week 26)
You gain weight.
You can feel the fetus moving.
The skin on your stomach stretches and may get dry. (Use lotion to lessen the chance of stretch marks.)
Your breasts get bigger. It helps to wear a supportive bra.
A small amount of thin fluid (called colostrum) may come out of your nipples.
You may experience ongoing heartburn, indigestion, and constipation.
You may get nosebleeds.
Your feet, hands, ankles and face may swell (this is called edema).
A dark line develops on your skin between your navel and your pubic area.
A "mask" or darker area or pigmentation may develop on your face. (It disappears after the pregnancy ends.)
The Third Trimester
(Week 27 - 40)
You can see the fetus move from the outside.
Your navel pushes out.
You begin to get backaches.
You begin to walk differently to accommodate the weight of the fetus.
You experience painless "practice" contractions.
You have shortness of breath.
Finally, labor and delivery!
Source:- http://www.epigee.org