Fetal Development

The growth of your baby is a continuous process that often conveys a sense of awe. The following information will help you understand your baby's rapid growth and highlights milestones in development. (Sizes and weights are approximate).

First Trimester


At the end of 4 weeks:
* Embryo is ¼ inch in length
* Heart, digestive system, backbone and spinal cord begin to form
* Placenta (sometimes called "afterbirth") begins developing
* The single fertilized egg is now 10,000 times larger than size at conception


At the end of 8 weeks:
* Embryo is 1-1/8 inches in length
* Eyes, nose, lips, tongue, ears and teeth are forming
* Penis begins to appear in boys
* Embryo is moving, although the mother cannot yet feel movement
* Heart is functioning




At the end of 12 weeks:
* Fetus is 2-½ to 3 inches long
* Weighs about 1/2 to 1 ounce
* Nails start to develop and earlobes are formed
* Fetus develops recognizable form
* Arms, hands, fingers, legs, feet and toes are fully formed
* Eyes are almost fully developed
* By this stage, a fetus has developed most of his/her organs and tissues
* Fetal heart rate can be heard at 10 weeks with a special instrument called a Doppler

Second Trimester


At the end of 4 months:
* Fetus is 6-½ to 7 inches long
* Weighs about 6 to 7 ounces
* Fetus is developing reflexes such as sucking and swallowing. Fetus may begin sucking his/her thumb
* Tooth buds are developing
* Sweat glands are forming on palms and soles
* Fingers are well defined
* Sex is identifiable
* Skin is bright pink, transparent and covered with soft, downy hair
* Although recognizably human in appearnace, the baby would not be able to survive outside the mother's body




At the end of 5 months:
* Fetus is 8 to 10 inches long
* Weighs about 1 pound
* Hair begins to grow on his/her head
* Soft, woolly hair called lanugo will cover baby's body (and some may remain until a week after birth when it is shed)
* Mother begins to feel fetal movement
* Internal organs are maturing
* Eyebrows, eyelids and eyelashes appear





At the end of 6 months:
* Fetus is 11 to 14 inches long
* Weighs about 1-¾ to 2 pounds
* Eyelids begin to part and eyes open occasionally for short periods of time
* Skin is covered with protective coating called vernix
* Fetus is able to hiccup

Third Trimester


At the end of 7 months:
* Fetus is 14 to 16 inches long
* Weighs about 2-½ to 3-½ pounds
* Taste buds have developed
* Fat layers are forming
* Organs are maturing
* Skin is still wrinkled and red
* If born at this time, he/she will be considered a premature baby and require special care





At the end of 8 months:
* Fetus is 16-½ to 18 inches long
* Weighs about 4 to 6 pounds
* Overall growth is rapid this month
* Tremendous brain growth occurs at this time
* Most body organs are now developed with the exception of the lungs
* Movements or "kicks" are strong enough to be visible from the outside
* Kidneys are mature
* Skin is less wrinkled
* Fingernails now extend beyond fingertips




At the end of 9 months:
* Fetus is 19 to 20 inches long
* Weighs about 7 to 7 ½ pounds
* Skin is pink and smooth
* The lungs are mature
* Baby is now fully developed and can survive outside mother's body
* He/She settles down lower in the abdomen in preparation for birth and may seem less active

For further information, review the video The Miracle of Life and the book A Child is Born by Lennart Nielson for a pictorial review of your baby's development. Both are available at Newborn Connections.