Embryonic & Fetal Development
Within 36 hours after fertilization, the embryo reaches a two-cell stage. Within two-weeks, it
becomes implanted in the uterine wall. At that time, heart tissue and blood cells are already
developing.
End of 1st Month
 The heart is formed and begins to beat at 3 ½ weeks
 Three parts of the brain are formed
 The backbone and spinal cord are forming
 The lungs and thyroid gland are developing
 Digestive system is starting to develop
 Some eye rudiments are present
 The placenta begins to form
 The single fertilized egg is now 10,000 times larger than size at conception
 The embryo measures about ¼ inch long
End of the 2nd Month
 Brain waves are evident
 Spine and nervous system are forming
 Heart and circulation are functioning (major blood vessels form)
 Internal organs continue to develop
 Limbs are forming, including the beginning of features such as
hands, fingers, knees, and toes
 Eyes are visible with fused eyelids
 Nose, lips, tongue, ears and teeth are forming
 Penis begins to appear in boys (gender isn’t detectable until the
end of the 3rd month)
 Baby is moving (mother cannot yet feel movement)
 The embryo measures about 1 to 1 ½ inches long and weighs 1/30 ounce
End of the 3rd Month
 The fetus develops a recognizable form
 Arms, hands, fingers, legs, feet and toes are fully formed
 Eyes are almost fully developed
 The uterus has now doubled in size. The fetus can squint, swallow and wrinkle its
forehead
 Earlobes are formed and ears continue to develop
 Muscular development is sufficient to open and close mouth and swallow
 Skin is evident and nails appear
 Heart beat is detectable and the heart rate can be heard at 10 weeks with a special
instrument called a Doppler
 Limbs are full formed, nails appear
 The fetus has developed most of his/her organs and tissues
 Lymph glands develop
 Bone marrow makes blood cells
 Placenta is fully formed
 The fetus measure about 2 ½ to 3 inches long and weighs
about ½ to 1 ounce
End of the 4th Month
 Fetus can suck thumb and urinate
 The face has human features (more recognizable); the head has hair, but it is
proportionally large
 The fetus is developing reflexes, such as sucking and swallowing and may begin sucking
his/her thumb
 Tooth buds are developing
 Bones are hardening, joints begin to form
 The digestive system is forming and the intestines are present. Meconium, the baby's first
stool, is present in the intestines as well.
 Sweat glands are forming on palms and soles
 Fingers and toes are well defined
 Skin is bright pink, transparent and covered with soft, downy hair
 External sex organs are identifiable (gender can be detected)
 Although recognizably human in appearance, the baby would not be
able to survive outside the mother's body
 The fetus weighs 4 to 8 ounces and measures 6 ½ to 10 inches
End of the 5th Month
 Fingernails begin to grow
 Fingerprints and footprints are present
 Eyelashes and eyebrows appear; the head is more in proportion to
the rest of the body
 Heartbeat can be heard
 Soft, fine, woolly hair called lanugo covers the body (some of this
hair may remain until a week after birth, when it is shed)
 The mother begins to feel fetal movement
 The baby can suck and swallow, and he/she may even be found
sucking his/her thumb
 Vernix, a white lanolin-like covering, appears on the baby to protect his/her skin
 The ears are developed and he/she may be able to hear people
 Your fetus measures 7 to 12 inches long and weighs ½ to 1 pound
End of the 6th Month
 Fingernails and toenails are complete
 The fetus can cry and kick
 The baby’s immune system is developing and he/she is
beginning to create her own antibodies
 The fetus has developed a hand grip reflex and startle reflex
 The lungs are beginning to develop and alveoli are forming
 He/she is growing and filling out, and he/she looks more and
more like the person she will be when she is born
 The fetus measures 9 to 14 inches long and weighs in at about
1 ¼ to 2 ¼ pounds
End of the 7th Month
 The eyes are open and he/she is able to cry
 The baby now uses the four senses of vision, hearing, taste (the taste buds have
developed), and touch
 The organs are maturing
 He/she may be very active now and others may be able to see her movements
 He/she may have hiccups, which will feel like a jumpy movement
 He/she is increasing in body fat (fat layers are forming) and her
bones are fully developed now
 Skin is still wrinkled and reddish/pink
 The fetus assumes upside down position
 If born at this time, baby will be considered a premature baby
and require special care
 The fetus measures 11 to 17 inches long and weighs around 2 ½ to 3 ½ pounds
End of the 8th Month
 Overall growth is rapid this month
 Tremendous brain growth occurs at this time (the bones of the head are soft)
 Most body organs are now developed with the exception of the lungs
 The baby absorbs a gallon of amniotic fluid per day; the fluid is
completely replaced every three hours.
 Movements or "kicks" are strong enough to be visible from the
outside, as the baby is becoming increasingly cramped for space and
keeping very active
 The baby sleeps most of the time now and has periods of REM sleep
 Kidneys are mature
 Fat deposits under the skin make skin less wrinkled
 Fingernails now extend beyond fingertips
 In males, the testes descend into the scrotum
 The fetus measures 13 to 18 inches long and weighs around 4 to 6 pounds
End of the 9th Month
 The lungs are mature
 Now it is fully developed and can survive outside the mother's body
 Skin is pink and smooth
 The baby settles down lower in the abdomen in preparation for birth
and may seem less active
 He/she should be facing head down in preparation for birth.
 Each baby’s weight and length varies considerably at birth, but typical
ranges include: 18 to 21 inches in length and a weight of 7 to 9 pounds
Credits/Resources (all of the above information came from the following sources):
Glencoe Human Sexuality
Health Teacher’s Book of Lists
http://www.babies.sutterhealth.org/babygrowth/fetaldev/
http://www.geocities.com/Wellesley/4375/process.htm (photos)
http://www.justmommies.com/articles/fetal_development.shtml