Stages of Pregnancy

  • During the first trimester, women experience hormonal changes affecting almost every organ system. Not having a menstrual period is a clear sign of pregnancy. Other symptoms associated with hormonal changes include: extreme tiredness; tender, swollen breasts; upset stomach with or without vomiting; food cravings; mood swings; constipation; frequent urination; headache; heartburn; weight gain or loss.

  • At the end of the first trimester, the fetus measures about 6 centimeters in length and weighs about 20 grams. At 12 weeks, the placenta, which is attached to the fetus via the umbilical cord (left), is fully-developed. The fetus is able to move its arms and legs, and its eyes have formed, although the eyelids remain sealed.

  • Most women find the second trimester of pregnancy to be easier than the first. Symptoms such as nausea and fatigue tend to go away, and the abdomen continues to grow to make room for the baby. Second trimester symptoms include: body aches; stretch marks on the abdomen, buttocks and thighs; darkening of the areolas and patches of darker skin on the face known as melasma (pictured).

  • By 20 weeks the fetus appears completely human, with fully developed lips, eyelids, eyebrows, external ears, fingers and toes. There is not much subcutaneous fat on the limbs or face, and the weight of the fetus is still less than 500 grams. Fine hair called lanugo has developed, and the head, still disproportionately large, grows more slowly than the body.

  • During the third trimester, many women find breathing difficult and notice they have to go to the bathroom even more often. Third trimester symptoms include: shortness of breath; heartburn; swelling of the ankles, fingers and face; hemorrhoids; breast tenderness and leakage of a watery pre-milk called colostrum; trouble sleeping; the fetus moving lower in the abdomen; and contractions signaling labor.

  • By 32 weeks the baby’s bones are fully formed, but still soft; the eyes open, close and sense changes in light; although the lungs aren’t fully formed, practice breathing movements occur; and lanugo begins to fall off. During the third trimester the baby gains weight quickly, about one-half pound a week.

  • As a pregnant woman nears her due date, the cervix becomes thinner and softer in a process called effacing. This is a normal, natural process that helps the birth canal to open during the birthing process. On average, full term babies weigh between 6 pounds 2 ounces and 9 pounds 2 ounces and are between 19 to 21 inches long at birth.

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Pregnancy is measured in trimesters from the first day of a woman’s last menstrual period (LMP) and normally lasts about 40 weeks from conception to the birth of the baby. This time is roughly divided into 3 periods: the first trimester, second trimester and third trimester. Learn more about the stages of pregnancy in this slideshow.

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