In the time it takes to count to 10, more than 60 women become pregnant around the world. Pregnancy is normally a 40-week journey, usually measured from the date of a woman's last menstrual period to the birth of her baby. It's a time of rapid development for the soon-to-be-baby, and sometime bewildering changes for the mother.
Pregnancy is divided into three periods, known as trimesters. Each lasts about 13 weeks. The trimesters are roughly equivalent to specific developmental stages.
First trimester: A baby's body and organ systems begin their initial development. This is the period during which most miscarriages and birth defects occur. It is also when women tend to experience morning sickness, fatigue, and other pregnancy-related symptoms. By the end of the first trimester, the average fetus is 3 inches long and weighs about an ounce.
Second trimester: During the second trimester, a baby grows skin and hair, and even develops fingerprints. A heartbeat can be heard with a stethoscope. For moms, morning sickness tends to fade, and sleep improves. But other problems, such as back pain, leg cramps, and heartburn, may appear. The baby's first movements are usually felt during the second trimester. By its end, the average baby is about 14 inches long and weighs more than 2 pounds. Babies delivered at the end of the second trimester may be able to survive with the help of medical technology.
Third trimester: The final stretch for baby and mother. It's a time of rapid growth and maturation for the baby. Toward the end of the third trimester, the baby usually moves into the "head down" position in preparation for birth. At 38 weeks, the baby is considered full term and can make its appearance at any time. Because the baby is getting so big, a mom can experience shortness of breath, hemorrhoids, and trouble sleeping. Toward the end of the third trimester, the average baby is 19 to 21 inches long and weighs between 6 and 10 pounds.