Major Milestones

Weeks 9-12

  • Length doubles between 9 and 12 weeks
  • Upper limbs develop to normal proportions, while lower limbs remain less developed
  • Male and female genitalia are recognizable by 12 weeks

Weeks 13-16

  • Rapid fetal growth occurs
  • Fetus double in size
  • Lanugo begins to grow, this is fine hair that grow on the fetal body
  • Fingernails are formed
  • Kidneys begin to secrete urine
  • Fetus begins to swallow amniotic fluid
  • Fetus appears human
  • Placenta is fully formed

Weeks 17-23

  • Fetal growth slows
  • Lower limbs are fully formed
  • Fetal body covered with lanugo,
  • Vernix caseosa, white cheesy substance, covers the body to protect the skin from amniotic fluid
  • Brown fat forms, fetuses are born with this type of fat to help keep them warm after delivery.

Weeks 24-27

  • Skin growth is rapid, and skin appears red and wrinkled
  • The eyes open and eyelashes an eyebrows are formed
  • The fetus becomes viable, able to live on own, at 26-27 weeks

Weeks 28-31

  • Subcutaneous fat is deposited
  • If the fetus is born at this time with immature lungs, respiratory distress syndrome may occur.

Weeks 32-36

  • Lanugo has disappeared from the body but remains on the head
  • Weight gain is steady
  • Fingernails are growing
  • The fetus has a good chance of surviving if born

Weeks 37-40

  • Subcutaneous fat builds, and fetal contours appear round
  • Both testes have descended in the male
  • The skull is fully developed

Reference:
Simpson, Kathleen Rice: Creehan, Patricia A. (2008). Perinatal Nursing. Lippincott Williams and Wilkins. Philadelphia, Pennyslvania