Stages of Fetal Development - Second Trimester

Stages of Fetal Development - Second Trimester

14 - 23 Weeks

WEEK 14
(16 weeks after the first day of the last normal menstrual period)

  • The fetus is about 43/4-inches from head to rump and weighs 4 ounces.
  • The head is erect and the arms and legs are developed.
  • The baby’s eyes have begun to face forward and slowly move, and the ears are close to reaching their final position.
  • The baby might be able to make sucking motions with his or her mouth.
  • Although still too slight to be felt, the baby’s movements are becoming coordinated and can be detected during ultrasound exams.

WEEK 16
(18 weeks after the first day of the last normal menstrual period)

  • The fetus is about 5-inches from head to rump and weighs about 8 ounces.
  • The skin is pink and transparent and the ears stick out from the head.
  • The baby might begin to hear.

WEEK 18
(20 weeks after the first day of the last normal menstrual period)

  • The fetus is about 61/4-inches from head to rump.
  • All organs and structures have been formed, and a period of simple growth begins.
  • Respiratory movements occur, but the lungs have not developed enough to permit survival outside the uterus.
  • By this time, the woman can feel the fetus moving.

WEEK 20
(22 weeks after the first day of the last normal menstrual period)

  • The fetus is about 71/2-inches from head to rump and weighs about 1 pound.
  • The baby has nails on its fingers and toes, fingerprints and perhaps some head and body hair.
  • This is the lowest limit of viability (meaning the baby may have a possibility of survival outside the woman's body with intensive care services).
  • There is little chance before this time that a baby could survive outside the woman’s body.
  • Eyebrows and lashes appear.
  • The baby now has increased muscle development and is more active.
  • The fetal heartbeat can be heard with a stethoscope.
By twenty weeks gestation, the unborn child has the physical structures necessary to experience pain. There is evidence that by twenty-weeks gestation unborn children seek to evade certain stimuli in a manner in which an infant or adult would stimuli.

WEEK 22
(24 weeks after the first day of the last normal menstrual period)

  • The fetus is about 81/4-inches from head to rump and weighs about 11/4-pounds.
  • Changes are occurring in lung development, so some babies are able to survive with intensive care services if born at this point.
  • The baby is regularly sleeping and waking.
  • Real hair is growing on his or her head.