29. The Fetal Period: Weeks 21 to Term

  1. Fetal period changes
    1. WEEKS 21 TO 25
      1. There is much weight gain; the body is proportioned; the skin is wrinkled but is very translucent and is pink to red in color, with blood in the capillaries visible
      2. If born at this time, the fetus usually dies due to an immature respiratory system
    2. WEEKS 26 TO 29
      1. The fetal eyes reopen, and the head and lanugo hair are well developed
      2. There is much subcutaneous fat formed, and the wrinkles of skin smooth out
      3. White fat increases to 5%
      4. The fetus is viable and can survive if born prematurely, but the mortality is high as a result of respiratory problems, even though the lungs and pulmonary vasculature are developed for gas exchange
      5. The CNS is mature and can control breathing and body temperature
    3. WEEKS 30 TO 34
      1. The skin is smooth and pink, and the arms and legs are round and full
      2. The body white fat is now about 7 to 8%
    4. WEEKS 35 TO 38
    5. AT BIRTH (TERM)
      1. Usually takes place about 266 days or 38 weeks after fertilization, or 280 days (about 40 weeks) from the onset of the last menstrual perio Variations are due to irregular menstrual periods and difficulty of counting and may be from 2 to 3 weeks
      2. Most fetuses are born within 10 to 15 days of the above times but may go to 276 to 286 days after fertilization
      3. Postmature infants are thin and have dry, parchmentlike skin
      4. For calculations of birth date: in the typical 28-day menstrual cycle, you count back 3 calendar months from the first day of the last menstrual period and then add 1 year and 1 week
      1. Amino acids and glucose (primary source of energy): derived from mother via placenta
      2. Insulin: for glucose metabolism and stimulation of fetal growth. Secreted by the fetal pancreas; little of the mother's insulin reaches the fetus normally
        1. Infants of diabetic mothers tend to be larger than normal
      3. Maternal malnutrition can cause reduced fetal growth
      4. Smoking can reduce fetal growth rate if in excess
      5. Multiple pregnancies: each fetus tends to be smaller than normal single births
      6. Impaired uteroplacental blood flow can cause fetal starvation and even fetal growth may decrease
      7. Placental dysfunction or defects may result in a growth decrease
      8. Genetic factors and chromosomal aberrations may lead to retarded fetal growth

the fetal period: weeks 21 to term: image #1