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
