Month 1

As the fertilized egg grows, a water-tight sac forms around it, gradually filling with fluid. This is called the amniotic sac, and it helps cushion the growing embryo.

The placenta also develops. The placenta is a round, flat organ that transfers nutrients from the mother to the baby, and transfers wastes from the baby.

A primitive face takes form with large dark circles for eyes. The mouth, lower jaw, and throat are developing. Blood cells are taking shape, and circulation will begin.

By the end of the first month, your baby is about 1/4 inch long - smaller than a grain of rice!

Month 2

Your baby's facial features continue to develop. Each ear begins as a little fold of skin at the side of the head. Tiny buds that eventually grow into arms and legs are forming. Fingers, toes and eyes are also forming.
The neural tube (brain, spinal cord and other neural tissue of the central nervous system) is well formed. The digestive tract and sensory organs begin to develop. Bone starts to replace cartilage. The embryo begins movement although the mother can not yet feel it.
By the end of the second month, your baby, now a fetus, is about 1 inch long, weighs about 1/3 ounce, and is virtually all head (1/3 of its body is head).

At about 6 weeks, your baby's heartbeat can usually be detected.

Month 3

By the end of the third month, your baby is fully formed. Your baby has arms, hands, fingers, feet and toes and can open and close its fists and mouth. Fingernails and toenails are beginning to develop and the external ears are formed. The beginnings of teeth are forming. Your baby's reproductive organs also develop, but the baby's gender is difficult to distinguish on ultrasound. The circulatory and urinary systems are working and the liver produces bile.
At the end of the third month, your baby is about 3-4 inches long and weighs about 1 ounce.

Since your baby's most critical development has taken place, your chance of miscarriage drops considerably after three months.

Month 4

Your baby's fingers and toes are well-defined; eyelids, eyebrows, eyelashes, nails and hair are formed. Teeth and bones become denser. Your baby can even suck his or her thumb, yawn, stretch and make faces.

The nervous system is starting to function. The reproductive organs and genitalia are now fully developed, and your health care provider can see on ultrasound if you are having a boy or a girl. Your baby's heartbeat may now be audible through an instrument called a Doppler.

By the end of the fourth month, your baby is about 6 inches long and weighs about 4 ounces.

Month 5

Hair is beginning to grow on your baby's head and lanugo, a soft fine hair, covers his or her shoulders, back, and temples. This hair protects your baby and is usually shed at the end of the baby's first week of life.
Your baby's skin is covered with a whitish coating called vernix caseosa. This "cheesy" substance, thought to protect baby's skin from long exposure to the amniotic fluid, is shed just before birth.
You may begin to feel your baby move, since he or she is developing muscles and exercising them. This first movement is called quickening.
By the end of the fifth month, your baby is about 10 inches long and weighs from 1/2 to 1 pound.
Now that you've read about your baby's development in the first 20 weeks, take this quiz to test your smarts!

Month 6

By the end of the sixth month, your baby is about 12 inches long and weighs about 2 pounds. His or her skin is reddish in color, wrinkled, and veins are visible through the baby's translucent skin. Baby's finger and toe prints are visible. The eyelids begin to part and the eyes open.
Your baby may respond to sounds by moving or increasing the pulse, and you may notice jerking motions if baby hiccups.
If born prematurely, your baby may survive after the 23rd week with intensive care.

Month 7

At the end of the seventh month, fat begins to be deposited on your baby. Your baby is about 14 inches long and weighs from 2 to 4 pounds. Your baby's hearing is fully developed and he or she changes position frequently and responds to stimuli, including sound, pain and light.

The amniotic fluid begins to diminish.

If born prematurely, your baby would likely survive after the seventh month.

Month 8

Your baby, who is now about 18 inches long and weighs as much as 5 pounds, will continue to mature and develop reserves of body fat. You may notice that your baby is kicking more. Baby's brain is developing rapidly at this time, and he or she can see and hear. Most internal systems are well developed, but the lungs may still be immature.

Month 9

Your baby continues to grow and mature: the lungs are nearly fully developed. Your baby's reflexes are coordinated so he or she can blink, close the eyes, turn the head, grasp firmly, and respond to sounds, light and touch.
You may notice that your baby moves less now since he or she is more confined in your uterus. Your baby's position changes to prepare itself for labor and delivery. The baby drops down in your pelvis, and usually his or her head is facing down toward the birth canal.
By the end of this month, your baby is about 18 to 20 inches long and weighs about 7 pounds.