- Baby is very active: kicking and punching with well formed arms and legs – strongly enough to temporarily “dent” the walls of the uterus. Fetal movement called “quickening” can be clearly felt by mom. Mom can now feel baby turn, kick and hiccup and may be able to identify a bulge as an elbow or head when she is at rest.
- Baby’s ears are almost fully developed – baby may respond to loud sounds by jumping.
- Hair is visible all over baby’s body.
- Testicles begin to descend from abdomen into scrotum in boys.
- Each side of the brain has a billion nerve cells now.
- Larynx (voice box) begins moving in a way similar to the movement seen during crying after birth.
- Baby weighs about 9 ounces and measures about 10 inches from head to heel.
- Between 18 and 21 weeks rapid eye movements begin. Rapid Eye Movement (REM), indicative of dreaming, is detectable and can be recorded. Baby’s sleep patterns begin: sleeping and waking, nestling in favorite / most comfortable position, stretching upon waking, exercising muscles energetically.
- Breathing patterns, body movements, and heart rate begin to follow daily cycles called circadian rhythms.
- Baby’s sense of hearing begins to function and the fetus starts responding to various sounds. The cochlea, the organ of hearing, reaches adult size.
- All skin layers and structures are complete; oil and sweat glands function and help to regulate body temperature. Delicate skin is protected from amniotic fluid by a greasy white substance called vernix which is absorbed into the skin soon after birth.
- Baby weighs slightly less than 1 pound and measures about 11 inches from head to heel.
Rapid eye movement begins, indicative of dreams.
With highly specialized medical care some babies can survive outside the womb by 20 weeks (22 LMP) with survival rates reported as high as 40%. Baby now feels pain more intensely than at any other time in development because while baby's nervous system has developed, natural pain inhibitors have not.