The first trimester
Babies grow at an amazing rate. By the time you have missed a menstrual period, the fertilized egg has been implanted in your uterus and the placenta has begun to form.
By six weeks your baby will be the size of a grain of rice, and by eight weeks your baby will have a face. The developing baby, called a fetus, will soon start to look like a baby, complete with eyelids and ears. All of the baby’s major organs and body parts are made during the first trimester -- or first three months of pregnancy. By the end of this trimester, your baby will be about 4 inches long, weigh 1 ounce, and have all of his fingers and toes.
- 6 Weeks – The brain and major organs begin to develop.
- 7 Weeks – The eyes begin to form.
- 8 Weeks – The ear structure is formed.
- 9 Weeks – The baby is able to move, although it’s too early to feel.
- 10 Weeks – The heart is beating.
- 11 Weeks – The placenta, or “afterbirth,” is totally functioning.
- 12 Weeks – The toes and fingers are formed.
The second trimester
During the second trimester (the fourth through the sixth month) your baby grows to a length of about 14 to 16 inches. During this time, the long bones (legs, arms) form, so it is important to include adequate amounts of calcium in your diet.
Other developments include:
- 15 Weeks – Fine hair called “lanugo” forms all over the baby’s body.
- 16 Weeks – The sex of the baby can be identified.
- 17-22 Weeks – You will probably begin to feel the baby move; This is called “quickening.”
- 20 Weeks – Hair on your baby’s head is beginning to grow.
- 24 Weeks – “Vernix”, a waxy, white substance that covers and protects your baby’s skin, is formed.
The third trimester
During the third trimester, or the seventh through the ninth month, your baby grows very quickly, gaining about a half pound each week. The baby’s kicks will be stronger; his organs are fully developed.
Other developments include:
- 28 Weeks – Your baby’s skin is red and wrinkled. His eyes begin to open and close. Surfactant, a substance needed for him to breathe on his own, is beginning to form. His hearing goes beyond your voice, and you may notice him respond to music with movement. His brain is growing rapidly.
- 29 Weeks – Body fat is beginning to form.
- 32 Weeks – The skin is less red and wrinkled; fingernails and toenails have begun to grow; he is now able to blink.
- 36 Weeks – Your baby is plump, generally weighing between 5-6 lbs. and measuring between 16-19 inches in length.
- 40 Weeks – Your baby is full term; the skin looks smooth and polished, the fine hair (lanugo) that covered his body is gone, and the nails extend beyond the fingers and toes; average weight is between 6-1/2 to 8 pounds; average length is between 19-21 inches.