Month 1 (weeks 1 through 4)
A water-tight sac forms around the egg, gradually filling with amniotic fluid and the placenta develops. In these first few weeks, a primitive face will take form with large dark circles for eyes. The tiny "heart" tube will beat 65 times a minute by the end of the fourth week.
By the end of the first month, the fetus is about 1/4 inch long – smaller than a grain of rice.
Month 2 (weeks 5 through 8)
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.
Bone starts to replace cartilage. At about 6 weeks, a heartbeat can usually be detected.
By the end of the second month, the fetus is about 1 inch long and weighs about 1/30 of an ounce.
Month 3 (weeks 9 through 12)
The arms, hands, fingers, feet and toes are fully formed. Fingernails and toenails are beginning to develop and the external ears are formed. The beginnings of teeth are forming under the gums.
By the end of the third month, the fetus is fully formed.
At the end of the third month, the fetus is about 4 inches long and weighs about 1 ounce.
Month 4 (weeks 13 through 16)
The fingers and toes are well-defined. Eyelids, eyebrows, eyelashes, nails and hair are formed. Teeth and bones become denser. The nervous system is starting to function.
The reproductive organs and genitalia are now fully developed.
By the end of the fourth month, the fetus is about 6 inches long and weighs about 4 ounces.
Month 5 (weeks 17 through 20)
The fetus is developing muscles and exercising them. This first movement can feel like a flutter.
Hair begins to grow on the head. The shoulders, back and temples are covered by a soft fine hair.
The skin is covered with a whitish coating.
By the end of the fifth month, the fetus is about 10 inches long and weighs from 1/2 to 1 pound.
Month 6 (weeks 21 through 24)
The finger and toe prints are visible. In this stage, the eyelids begin to part and the eyes open.
The fetus responds to sounds by moving or increasing the pulse. You may notice jerking motions if the fetus hiccups.
By the end of the sixth month, the fetus is about 12 inches long and weighs about 2 pounds.
Month 7 (weeks 25 through 28)
At this point, hearing is fully developed. The fetus changes position frequently and responds to stimuli, including sound, pain and light. The amniotic fluid begins to diminish.
At the end of the seventh month, the fetus is about 14 inches long and weighs from 2 to 4 pounds.
Month 8 (weeks 29 through 32)
You may notice more kicking. The brain developing rapidly at this time, and the fetus can see and hear. Most internal systems are well developed, but the lungs may still be immature.
The fetus is about 18 inches long and weighs as much as 5 pounds.
Month 9 (weeks 33 through 36)
The lungs are close to being fully developed at this point.
The fetus has coordinated reflexes and can blink, close the eyes, turn the head, grasp firmly, and respond to sounds, light and touch.
The fetus is about 17 to 19 inches long and weighs from 5 ½ pounds to 6 ½ pounds.
Month 10 (Weeks 37 through 40)
At this point, The fetus's position may have changed to prepare for birth. You may feel very uncomfortable in this final stretch of time as the fetus drops down into your pelvis and prepares for birth. Your baby is ready to meet the world at this point.
They are about 18 to 20 inches long and weigh about 7 pounds.