The average pregnancy lasts about 40 weeks from the date of your last normal menstrual period, according to the KidsHealth website. The 40-week pregnancy is broken down into trimesters. Health-care professionals use trimesters to group specific milestones for monitoring the health of the mother and baby and gauging the advancement of the pregnancy. The due date provided by your obstetrician is only an estimate. Most women deliver 38 to 42 weeks after the last menstrual period, KidsHealth adds.
First Trimester
The first trimester of your pregnancy includes the first three months, or weeks one through 12.
Your body undergoes hormonal changes which cause fatigue, swollen and tender breasts, mood swings and morning sickness. During this period you might experience headaches, cravings and frequent urination. Your baby changes from an embryo to a fetus and develops facial features and all major organs, including external sex organs. He has tooth buds and can make a fist.
Second Trimester
Your second trimester covers the second three months of your pregnancy, or weeks 13 through 28. The U.S. government's WomensHealth website reports that most women feel they have an easier time during the second trimester. You might notice less fatigue and nausea, but your body is making room for the baby, so you begin to experience aches, pains and discomfort. Changes in your skin include stretch marks and itchiness on your hands and feet. You might notice dark skin patches on your face, called the mask of pregnancy. Your baby begins to move; her brain is developing rapidly, and she can hear. Your doctor can hear her fetal heartbeat.
Third Trimester
The last three months of your pregnancy make up your third trimester, or weeks 29 through 40. Your discomfort increases as your growing baby puts more pressure on your organs. You might experience swelling of your face or ankles, shortness of breath and trouble sleeping. Your baby drops to a lower position and effacing, the thinning of your cervix, takes place as your body prepares to give birth. Your baby has fully formed bones, begins to store certain nutrients and has an increase in body fat. You might have a few episodes of false labor and, eventually, true labor, which will progress through full cervical dilation, delivery of the infant and passage of the placenta.
