Pregnancy is typically divided into three stages, or trimesters, each lasting about 13 weeks. These trimesters bring new experiences for both the expectant mother and the fetus. Pregnancy calculations start from the beginning of a woman's last menstrual period. Therefore, week 1 and 2 occur before an egg has even been released from an ovary. A normal pregnancy lasts about 40 weeks.
The First Trimester
Lasting from the first day of the last period until about week 13, the first trimester is a critical time for the developing fetus. During this stage, the fetus undergoes organogenesis, or the formation of the organs of the body. For instance, the heart begins beating by week 6, BabyCenter reports. Since so much critical development is occurring in this stage, it is vitally important for the woman to avoid alcohol, street drugs, and to get approval from her doctor for any medication she takes, including over-the-counter remedies. As a woman's body adjusts to pregnancy, many women experience fatigue, frequent urination, swollen breasts and headaches, according to the website Parenting. About three-quarters of pregnant women suffer from morning sickness, which can appear at any time of the day or night and may or may not involve vomiting. Morning sickness may begin around week 6 and subside by week 12, according to the American Pregnancy Association. Some women, however, continue to experience morning sickness throughout their pregnancies.
The Second Trimester
The second stage of pregnancy lasts from about week 14 through week 27. Women usually feel their best during this stage, says BabyCenter. Morning sickness has passed, fatigue has decreased, and the woman is not yet large enough to be uncomfortable. The baby's first movements will also be felt, reports Parenting. By now the fetus resembles a human being, can wiggle fingers and toes, "breathe" in amniotic fluid, and suck. The major organ systems and parts of the body have been formed, although the lungs still have much development to undergo. Growth picks up during this trimester, and what probably remained hidden during the first trimester becomes obvious over the course of this stage.
The Third Trimester
The major development of the third trimester, which stretches from week 28 until birth, is growth. The fetus begins this stage weighing about 1.5 pounds and stretching about 14.8 inches in length, according to BabyCenter. Compared to birth stats, clearly there is much weight and length gained during this trimester. Most women gain about 11 pounds in these final 3 months, BabyCenter reports. As a result, women often become increasingly uncomfortable during the final trimester. Swelling of legs and ankles may occur, fatigue may return, and difficulty sleeping may set in as the belly becomes larger. Barring any difficulties, the woman will emerge from this stage with a beautiful addition to the family lying in her arms.
