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Fetal Development

Second Trimester

14 weeks after conception
(16 weeks after the last menstrual period)

  • The fetus is about 4 ¾ inches from crown to rump and weighs about 3 ½ ounces.
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  • The head is more erect and the arms and legs are developed.
  • Limb movements become more coordinated because joints will now function.

16 weeks after conception
(18 weeks after the last menstrual period)

  • The fetus is about 5 ½ inches long from crown to rump and weighs between 6 and 7 ounces.
  • The skin is transparent. Blood vessels are very easily seen through the skin.
  • Hair and nails begin to grow.
  • The fetus can now blink, grasp, and move the mouth.

18 weeks after conception
(20 weeks after the last menstrual period)

  • The fetus is about 6 ½ inches long from crown to rump and weighs about 10 ounces.
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  • All organs and structures have been formed and a period of simple growth begins.
  • The skin is covered by vernix, a waxy substance that protects the skin.
  • Most women feel the fetus moving or kicking.
  • The sex of the fetus can now often be more readily identified by ultrasound.
  • Some experts have concluded the fetus is capable of feeling physical pain at about this time of development; other experts have concluded the fetus feels pain during later stages of development. This issue can be explored in the reference section of this website.

20 weeks after conception
(22 weeks after the last menstrual period)

  • The fetus is about 7 ½ inches long from crown to rump and weighs from 14 to 16 ounces (1 pound).
  • The fetus is more active, kicking, sucking, and turning in the uterus.
  • A period of extremely rapid brain development is beginning.
  • The eyelids, eyebrows, and fingernails are well developed.
  • Survival rates for fetuses born at 22 weeks' gestation are low.

22 weeks after conception
(24 weeks after the last menstrual period)

  • The fetus is about 8 ½ inches long from crown to rump and weighs about 1 ¼ pounds.
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  • The bones of the ears harden, enabling sound conduction. The fetus can now hear voices or sounds of its mother's breathing or heartbeat.
  • The proportions of the face and body begin to assume the appearance of an infant near its due date.
  • A period of substantial weight gain is beginning; fat layers are starting to form.
  • Lungs are still immature; a fetus born at this time will attempt to breathe, but is not likely to survive without very intensive care. In Alaska, with optimal care, the survival rate of fetuses born at 23 weeks gestation is approximately 63%. If born at 24 weeks gestation, survival odds improve to 70%.

24 weeks after conception
(26 weeks after the last menstrual period)

  • The fetus is about 9 inches long from crown to rump and weighs 1½ to 1 ¾ pound.
  • The body is lean and the skin appears wrinkled due to the lack of body fat.
  • In Alaska, with optimal care, survival is 80% likely for fetuses born at this gestational age.

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