Weeks 1-4
Weeks 5-8
Growth Milestones from 9 weeks to 38 weeks: Monthly
Weeks 9-12
Weeks 13-16
Weeks 17-20
Weeks 21-25
Weeks 26-29
Weeks 30-34
Weeks 35-38

Within three weeks, what started out as a single cell has grown to millions of cells that now begin to differentiate into three types of cells: those that will become the nervous system, skin, and hair; those that will make up the gastrointestinal tract and those that will form the circulatory, genito-urinary and musculo-skeletal systems. By the end of the third week, a rudimentary heart tube begins to beat and circulate blood. You're just beginning to feel pregnant and already the baby making is well under way.

Even though you don't look any bigger, your baby is rapidly growing. Check out the ten growth milestones:

1. By the end of the fifth week, baby is the size of a green pea (or about 0.4 inches).
2. Pits that become the eyes, ears, nose and mouth begin to show.
3. More than one million new cells are added to baby's growing body each minute.
4. By six weeks, baby is ½ inch long, and ultrasound can show a fluttering heartbeat of about 140 to 150 beats per minute (twice as fast as yours).
5. At seven weeks, baby is around an inch long or the size of a small olive.
6. Elbow, wrist and knee joints are obvious.
7. Researchers estimate that by seven weeks, one hundred thousand new nerve cells are created every minute.
8. At eight weeks, baby is around the size of a large olive at 1½ inches long and ½ ounce in weight.
9. All the internal organs that will be present in the fully-grown infant have been formed by eight weeks.
10. Developing baby is now called a "fetus" and is beginning to look like a miniature human being.

During this month, baby more than doubles his length and weight, going from 1 1/2 inches at the end of the second month to 4 to 5 inches long by the end of the third; he will weigh from one-half to one ounce. Let's look at 10 growth milestones:

1. All of baby's organs are formed, and they will continue to grow and develop during the rest of the time in the womb.
2. Baby's liver, spleen, and bone marrow start making blood cells this month.
3. Baby's teeth begin to form; by the end of this month baby will have twenty little tooth buds beneath his gums.
4. Fingernails, toenails, and rudimentary hair appear.
5. Baby's intestines, previously part of the umbilical cord, now move into the abdominal cavity and become covered with skin.
6. The tongue and vocal cords form this month.
7. The circulatory system is operating, and heart valves are now developing, meaning a heartbeat can be detected by Doppler ultrasound.
8. The external genitalia differentiate clearly into male and female so that by the end of the month ultrasound pictures can often reveal whether baby is a boy or a girl.
9. By twelve weeks the head is around a third of the size of the body.
10. Baby's tiny feet can now kick, but you are unlikely to be able to feel it yet.

By the end of the 16th week, you can easily feel your grapefruit-sized uterus midway between your pubic bone and your navel. Let's look at 10 growth milestones during this month:

1. Your little "peach" is about the size of a peach!
2. Baby doubles her length and nearly quadruples her weight.
3. She is around five inches long and weighs around four ounces at the end of the 16th week.
4. Her arms lengthen this month and she can flex her arms, clasp her hands, and suck her thumb. Her legs lengthen, and kicking intensifies (you probably don't feel it yet).
5. Her bones (arms, hands, and legs) form and are visible on x-ray or ultrasound.
6. Baby "breathes" amniotic fluid in and out through the developing air passages and tiny sacs in her lungs.
7. Her external ear folds are becoming more developed, as is her hearing, enabling her to react to sounds.
8. She develops her own unique fingerprints.
9. Blood vessels proliferate at a rapid rate and show through baby's thin, still transparent skin.
10. The placenta becomes the prime producer of pregnancy hormones you will continually need to nourish your baby and yourself, and your baby now free floats in her own bubble of amniotic fluid, contained in an amniotic sac. By the 16th week, there is enough amniotic fluid for doctors to safely enter the fluid- filled sac by a procedure called amniocentesis.

By the end of this month you can feel your cantaloupe-sized uterus at the level of your navel. Other growth milestones include:

1. Your baby weighs around three-quarters of a pound, and measures between 8-10 inches long. This is about half the length baby will be at birth.
2. Baby's legs, now around the size of your little finger, continue growing, become more muscular, and make their presence felt as tiny flutter kicks.
3. He waves his growing, but still tiny, arms. On ultrasound, you may see him sucking his thumb and making a fist.
4. Baby hair is beginning to appear on his upper lid, eyebrows, and head.
5. His skin, previously thin and transparent, now begins to accumulate fat deposits.
6. Baby's oil glands start to secrete a waxy substance that mixes with his dead skin cells to form a cheesy coating, called the Vernix caseosa, which acts like a sort of wetsuit protecting the little swimmer's skin from chapping.
7. Fine, temporary hair—called lanugo (meaning "wool")—covers most of his body and helps to hold the vernix on the skin.
8. Baby's digestive system functions better now, and he regularly swallows amniotic fluid and urinates into it.
9. By this month, baby's middle ear structures have formed, enabling baby to hear sound.
10. Still, baby cannot yet survive outside the womb at this stage because his lungs are still undeveloped.

Check out the 10 growth milestones for baby:

1. By the end of this month baby weighs around 1-1/4 to 1-1/2 pounds.
2. Baby is around a foot long.
3. Increasing fat deposits beneath the skin cause her to take on a more plump, though still wrinkly, appearance.
4. Fingernails and eyelashes develop.
5. Scalp hair increases.
6. She now has a more recognizable baby face.
7. The vernix caseosa now covers the skin completely, like a layer of thin, whitish paste.
8. By 24th weeks, baby's nostrils open.
9. Her lungs begin to develop air sacs, called alveoli, though not enough of them to sustain breathing outside the womb.
10. Baby still needs the nourishment of her mother's womb! If she were born now her breathing would have to be assisted.

How does baby grow this month? Check out the following growth milestones:

1. By the end of this month baby weighs around 2 to 2-1/2 pounds and measures around fourteen inches long.
2. During this month baby has a growth spurt, gaining around a pound.
3. Fat deposits smooth out some of the previous wrinkles, giving baby a more filled out appearance, but he is still much skinnier than he will be at birth.
4. Baby is getting stronger! His limbs are longer, stronger, and these delightful little kicks make more of an impression in your abdomen.
5. Baby's eyelids open. Baby can now see, hear, smell, and taste.
6. Baby's bone marrow now takes over from the spleen as the major site of red blood cell production.
7. At this stage, baby moves vigorously and responds to touch and sound.
8. Baby gets smarter as major changes occur throughout her nervous system. Nerve fibers are clothed in a fatty layer called myelin that allows nerve impulses to travel faster.
9. Cells lining the rapidly budding alveoli (air sacs in baby's lungs) begin to secrete a soapy substance called surfactant that keeps these air sacs from collapsing—similar to the substance that keeps the soap bubble expanded. Depending on how well developed are the alveoli and surfactant secretion, if baby were born now, she may be able to sustain air breathing and life outside the womb.
10. Before the seventh month, most babies choose to lie in the breech position because it's easier for them to rest comfortably in the pear-shaped uterus, but most will flip to the head-down position by 34 weeks.

Let's look at the ten growth milestones baby is now making:

1. By the end of this month baby weighs from 3-4 pounds and is 16-18 inches long.
2. Fat deposits double, giving baby a more filled-out appearance.
3. Her skin begins to shed the silky, lanugo hair that covered the skin.
4. The hair on her eyelids and eyebrows grows longer.
5. Some babies sprout a full head of hair.
6. She can blink her eyes in reaction to outside light.
7. Baby has rapid brain growth and experiences definite REM and non-REM sleep stages.
8. Hiccups, which a mother may experience as sudden jerks, are common now.
9. Baby becomes more aware of her outside world and can react to its stimuli.
10. If she is born now, your baby may be able to breathe outside the womb on her own without medical assistance.

Wow! It's almost time, to greet baby into her new world. What is happening now?

1. Baby weighs from 6 to 7 ½ pounds.
2. She measures 18 to 20 inches.
3. This is her "finishing" stage, and baby gains a tremendous amount of subcutaneous fat, filling him out for birth.
4. The lanugo hair has disappeared.
5. Some of the vernix caseosa has disappeared, and it seems that just enough of this cheesy substance remains to lubricate him for a smoother passage during birth.
6. By this time baby has pretty much run out of room and is tucked up like a little ball.
7. During the final weeks inside the womb, baby sucks, swallows, breathes, and blinks.
8. He steps, turns his head, and sucks his thumb.
9. He grasps and clasps his hands, practicing all the movements he will need after he makes his appearance in the world.
10. The air sacs of his lungs are now lined with a substance called surfactant, that keep the lungs expanded after each breath, enabling nearly all babies born at this stage (even early in this stage) to breathe air outside the womb.