Welcome to our group web site.

WEEK 3 

What's going on in your womb now? A lot. Your baby-in-the-making is just a tiny ball consisting of several hundred cells that are multiplying madly. Once the ball of cells (called a blastocyst) takes up residence in your uterus, the part of it that will develop into the placenta starts producing the pregnancy hormone hCG (human chorionic gonadotropin), which tells your ovaries to stop releasing eggs and triggers increased production of estrogen and progesterone (which keep your uterus from shedding its lining — and its tiny passenger — and stimulates placental growth). HCG is the hormone that turns a pregnancy test positive; by the end of this week, you may be able to take one and get a positive result! (If your test is negative and you still haven't gotten your period in two or three days, try again then.)

Meanwhile, amniotic fluid is beginning to collect around your ball of cells in the cavity that will become the amniotic sac. This fluid will cushion your baby in the weeks and months ahead. Right now, your little blastocyst is receiving oxygen and nutrients (and discarding waste products) through a primitive circulation system made up of microscopic tunnels that connect your developing baby to the blood vessels in your uterine wall. The placenta won't be developed enough to take over this task until the end of next week.

WEEK 4 

This week marks the beginning of the embryonic period. From now until ten weeks, all of your baby's organs will begin to develop and function. As a result, this is the time when she'll be the most vulnerable to anything that might interfere with her development.

Right now your baby is an embryo consisting of two layers: the epiblast and the hypoblast, from which all her organs and body parts will develop. The primitive placenta is also made up of two layers at this point. Its cells are tunneling into the lining of your uterus, creating spaces for your blood to flow into so that the developed placenta can provide nutrients and oxygen to your growing baby when it starts to function at the end of this week. Also present now are the amniotic sac that will house your baby, the amniotic fluid that will cushion her as she grows, and the yolk sac that produces your baby's red blood cells and helps deliver nutrients to her until the placenta is ready to take over this duty.

WEEK 5 

Deep in your uterus your embryo is growing at a furious pace. At this point he's about the size of a sesame seed, and he looks more like a tiny tadpole than a human. He's now made up of three layers — the ectoderm, mesoderm, and endoderm — that will later form his organs and tissues. The cells are forming for his major organs, including his kidneys and liver, and his neural tube is beginning to develop. This neural tube — from which your baby's brain, spinal cord, nerves, and backbone will sprout — develops in the top layer, called the ectoderm. This layer will also give rise to his skin, hair, nails, mammary and sweat glands, and tooth enamel. His heart and circulatory system begin to form in the middle layer, or mesoderm. (This week, in fact, his tiny heart begins to divide into chambers and beat and pump blood.) The mesoderm will also form your baby's muscles, cartilage, bone, and subcutaneous (under skin) tissue. The third layer, or endoderm, will house his lungs, intestines, and rudimentary urinary system, as well as his thyroid, liver, and pancreas. In the meantime, the primitive placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already on the job.

WEEK 6 

The cells that will make up all of your baby's body parts and systems are dividing furiously as her body begins to take shape. Right now she's about the size of a small lentil bean (4 to 5 millimeters across). If you could see through your uterine wall, you'd find an overlarge head and dark spots where her eyes and nostrils are beginning to take shape. Shallow pits on the sides of her head mark her developing ears, and her arms and legs appear as protruding buds. Her hands and feet look like paddles, with thick webbing between the developing digits, but her fingers and toes will soon become more distinct. Below the opening that will later be your baby's mouth, there are small folds where her neck and lower jaw will eventually develop. (Inside, her tongue and vocal cords are just beginning to form.)

Your baby's heart (which is starting to divide into the right and left chambers) is beating about 100 to 130 beats per minute — almost twice as fast as yours — and blood is beginning to circulate through her body. Her intestines are developing and tiny breathing passages are beginning to appear where her lungs will be. She's also starting to build muscle fibers and, halfway through this week, she'll likely start moving her tiny limbs. Unfortunately, you'll probably have to wait until you're several weeks into your second trimester before you get to enjoy feeling your baby's calisthenics.

WEEK 7 

Your baby still appears to have a small tail (actually, it's an extension of his tailbone), which will disappear in the next few weeks. But that's the only thing getting smaller. Now almost half an inch long — roughly the size of a raspberry — he has elbow joints and distinct, slightly webbed fingers and toes. In his oversized head, both hemispheres of his brain are developing. His teeth and the inside of his mouth are forming, and his ears continue to develop. Eyelid folds partially cover his tiny peepers, which already have some color, and the tip of that nose you'll be tweaking someday is emerging. His skin is paper-thin and his veins are clearly visible.

Your little one also has an appendix and a pancreas, which will eventually produce the hormone insulin to aid in digestion. His liver is busy producing red blood cells, and a loop of your baby's growing intestines is bulging into his umbilical cord, which now has distinct blood vessels to carry oxygen and nutrients to and from his tiny body. You can't feel his gyrations yet, but your baby is like a little jumping bean, moving in fits and starts around his watery home.

WEEK 8 

Your baby is now 5/8 of an inch long, about the size of a kidney bean. She's constantly moving and shifting, although you won't be able to feel these womb wiggles for several weeks yet. Her embryonic tail is disappearing, and her eyelids practically cover her eyes. Still slightly webbed, her fingers and toes are growing longer. Her arms have lengthened, too, and her hands are now flexed at the wrist and meet over her heart. Her knee joints have formed, and her feet may be long enough to meet in front of her body. With her trunk straightening out, her head is more erect. Breathing tubes extend from her throat to the branches of her developing lungs. The nerve cells in her brain are also branching out to connect with one another, forming primitive neural pathways. Though you may be daydreaming about your baby as one gender or another, the external genitals still haven't developed enough to reveal whether you're having a boy or a girl.

WEEK 9 

Your new resident is nearly an inch long — barely the size of a grape — and weighs just a fraction of an ounce, but he's poised for rapid weight gain now that his basic physical structure is in place. He's also starting to look more and more human. His embryonic "tail" is now completely gone and his body parts — including organs, muscles, and nerves — are kicking into gear.

His eyelids are fused shut and won't open until 27 weeks. He has earlobes, and by week's end, the inner workings of his ears will be complete. His upper lip is fully formed, too, and his mouth, nose, and nostrils are more distinct. The tips of his fingers are slightly enlarged where his touch pads are developing. All major joints — his shoulders, elbows, wrists, knees, and ankles — are working, enabling your baby to move his limbs. As for his heart, it has divided into four chambers now, and the valves have started to develop. External sex organs are there, but won't be distinguishable as male or female for another few weeks.

WEEK 10 

Your baby is no longer an embryo! Though she's barely the size of a kumquat — just an inch or so long, crown to bottom — and weighs less than a quarter of an ounce, she now has completed the most critical portion of her development. This is the beginning of the so-called fetal period, a time when the tissues and organs in her body rapidly grow and mature. Her vital organs — the liver, kidney, intestines, brain, and lungs — are now in place and starting to function (although they'll continue to develop throughout your pregnancy). Her liver continues to make blood cells, and the yolk sac, which previously supplied these cells, is no longer needed and begins to disappear.

During the next three weeks, your baby's length will more than double to nearly 3 inches. Her head is proportionately smaller now than it was a few weeks ago, but it's still almost half the length of her entire body. Her forehead temporarily bulges with her developing brain and sits high on her head; it will later recede to give her a more human appearance. Each day, more minute details — including tiny fingernails, toenails, and peach-fuzz hair — start to appear on her body. Her fingers are now completely separated; her arms bend at the elbow and curve slightly; her hands are flexed at the wrist and meet over her heart; her legs are lengthening; and her feet may be long enough to meet in front of her body. She is busily swallowing amniotic fluid and kicking her legs.

If you could take a peek at your baby this week, you'd be able to clearly see the outline of her spine through her parchment-thin skin. Spinal nerves are beginning to stretch out from her spinal cord.

WEEK 11 

Your fig-sized baby is now fully formed — measuring 1 1/2 inches long and weighing in at a quarter of an ounce. His skin is still transparent, allowing many of his blood vessels to show through. Some of his bones are beginning to harden, and tiny toothbuds are starting to appear under his gums. His fingers and toes have separated, and he may soon be able to open and close his fists. He's already busy kicking and stretching, and his tiny movements are so fluid they look like water ballet. These movements will increase as his body grows and becomes more developed and functional. As his diaphragm develops, your tiny tenant may also start to get the hiccups. Because he's still so small, though, you won't feel any of his workouts or intrauterine gulps until sometime between weeks 16 and 20.

WEEK 12 

Your baby's hit the 2-inch mark (about the size of a lime) and weighs half an ounce. Her face is beginning to look more human. Her eyes, which started out on the sides of her head, have moved closer together on her face, and her ears are near their final positions on the sides of her head. Your baby's intestines, which have grown so rapidly that they protrude into the umbilical cord, will start to move into her abdominal cavity about now. Her kidneys are secreting urine into her bladder. Her nerve cells have been multiplying rapidly, and synapses (neurological pathways in the brain) are forming. Your baby may have acquired more reflexes by now, including sucking, and she'll even squirm if you prod your abdomen, though you still won't be able to feel her movement for several weeks.

WEEK 13 

Your belly may soon be big enough to announce to the world that you're expecting, but your baby is still tiny. In fact, he's only about 3 inches long crown to rump — roughly the size of a jumbo shrimp — and weighs just about an ounce. Despite the small proportions, there's a fully formed baby inside your womb now. Much more proportional than it was a few weeks ago, his head is now only about a third the size of his body. His tiny, unique fingerprints are already in place. His kidneys and urinary tract are functional, and he's starting to urinate out the amniotic fluid he's been swallowing. As you start your second trimester, most of your baby's critical development will be completed, and your odds of miscarriage will drop considerably.

WEEK 14 

Head to bottom, your baby's 3 1/2 inches long — about the length of a lemon — and weighs about 1 1/2 ounces. Her body's growing faster than her head, which now sits upon a more well-defined neck. By the end of this week, her arms will have lengthened and will be in proportion to the rest of her body. (Her legs still have some growing to do, though.) She's starting to develop an ultra-fine, downy covering of hair all over her body (called lanugo). Her liver starts secreting bile this week, a sign that it's already functioning properly, and her spleen starts contributing to the production of red blood cells. She's also producing and discharging urine into the amniotic fluid, a normal process that she'll keep up until birth. You still can't feel your baby's movements, but her hands and feet (which are now half an inch long) are more flexible and active. Thanks to brain impulses, her little facial muscles are getting a workout as she squints, frowns, and grimaces. She can grasp now, too, and she may be able to suck her thumb.

WEEK 15 

At around 4 inches long, crown to rump, your baby now weighs about 2 1/2 ounces. He's busy inhaling and exhaling amniotic fluid, which will help develop the air sacs in his lungs. His legs are growing longer than his arms now, and he can move all his joints and limbs. That means his hands are more functional, too. Sweat glands are appearing, and although his eyelids are fused shut, he can sense light. If you shine a flashlight at your tummy, he's likely to move away from the beam. There's not much for your baby to taste at this point, but his taste buds are beginning to form. And if you have an ultrasound, you may be able to find out whether your baby's a boy or girl! (Don't be disappointed if it remains a mystery, though. Nailing down the gender depends somewhat on how clear the picture is and the position of your baby during the ultrasound; he may be curled or turned in such a way as to keep you in suspense.)

WEEK 16 

At 4 1/2 inches long (head to bottom) and 3 1/2 ounces, your baby is about the size of an avocado. In the next three weeks, she'll go through a tremendous growth spurt, though, doubling her weight and adding inches to her length. Her lower limbs are much more developed now. Her head is more erect than it has been, and her eyes have moved toward the front of her head. Your baby's ears are close to their final position, too. Some of her more advanced body systems are working, including her circulatory system and urinary tract. Her heart is now pumping about 25 quarts of blood each day, circulating her total blood volume through her body many times. (By the end of your pregnancy, this will increase to about 190 quarts.) The patterning of her scalp has begun, though her hair isn't recognizable yet. Although closed, her eyes are moving (slowly), and she's even started growing toenails.

WEEK 17 

Your baby weighs about 5 ounces now, and he's around 5 inches long — about the size of a large onion. He can move his joints, and his skeleton — until now rubbery cartilage — is starting to harden to bone. His sense of hearing is also developing. The umbilical cord, his lifeline to the placenta, is growing stronger and thicker.

WEEK 18 

Head to bottom, your baby is approximately 5 1/2 inches long (about the length of a large sweet potato) and she weighs almost 7 ounces. She's busy flexing her arms and legs — movements that you'll likely start noticing more and more. Her blood vessels are visible through her thin skin and her ears are now in position and stand out from her head. Myelin (a protective covering) is beginning to form around her nerves, a process that will continue for a year after she's born. If you're having a girl, her uterus and Fallopian tubes are formed and in place. If your baby is a boy, his genitals are noticeable, though he may hide them from you during an ultrasound.

WEEK 19 

Your baby weighs about 8 1/2 ounces, and he measures 6 inches, head to bottom — about the length of a small zucchini. His arms and legs are in the right proportions to each other and the rest of his body now. His kidneys continue to make urine, and the hair on his scalp is sprouting. This is a crucial time for sensory development: Your baby's brain is designating specialized areas for smell, taste, hearing, vision, and touch. If your baby is a girl, she has an astonishing six million eggs in her ovaries. They'll dwindle to fewer than two million by the time she's born.

WEEK 20 

Your baby weighs about 10 1/2 ounces now. She's also around 6 1/2 inches long from head to bottom, and about 10 inches from head to heel. (For the first 20 weeks, we use measurements taken from the top of the baby's head to her bottom — known as the "crown to rump" measurement. After that, we use measurements from head to toe. This is because a baby's legs are curled up against her torso during the first half of pregnancy and are very hard to measure.)

A greasy white substance called vernix caseosa coats her entire body to protect her skin during its long submersion in amniotic fluid. (This slick coating also eases the journey down the birth canal.)

Your baby is swallowing more, which is good practice for her digestive system. She's also producing meconium, a black, sticky substance that's the result of cell loss, digestive secretion, and swallowed amniotic fluid. This meconium will accumulate in her bowels, and you'll see it in her first messy diaper (although a few babies pass it in utero or during delivery).

WEEK 21 

Your baby now weighs about three-quarters of a pound and is approximately 10 1/2 inches long. His eyebrows and eyelids are fully developed. And you can certainly feel him move. He's oblivious to your schedule, though, so don't be surprised if he starts working out just when you're settling down for the night. If you're having a girl, her vagina is formed now, though it will continue to develop until birth.

WEEK 22 

Your baby now looks like a miniature newborn, checking in at 10.9 inches and almost 1 pound. Her skin will continue to appear wrinkled until she gains enough weight to fill it out, and the fine hair (lanugo) that covers her head and body is now visible. Her lips are becoming more distinct, and the first signs of teeth are appearing as buds beneath her gum line. Her eyes are developed, though the iris (the colored part of the eye) still lacks pigment. Eyelids and eyebrows are in place, and her pancreas, essential for hormone production, is developing steadily.

WEEK 23 

Your baby is more than 11 inches long and weighs just over a pound. His skin is red and wrinkled. Blood vessels in his lungs are developing to prepare him for breathing. He can swallow, but he normally won't pass his first stool (called meconium) until after birth. Loud noises heard often in utero — such as your dog barking or the roar of a vacuum cleaner — probably won't faze your baby when he hears them outside the womb.

WEEK 24 

Your baby's growing steadily, gaining about a quarter of a pound since last week, when she was just over a pound. Since she's almost a foot long, that makes a pretty lean figure, but her body is filling out proportionally and she'll soon put on more baby fat. Your baby's skin is thin, translucent, and wrinkled, her brain is growing rapidly, and her taste buds are developing. Her lungs are developing "branches" of the respiratory "tree" and cells that produce surfactant, a substance that helps the air sacs inflate easily.

WEEK 25 

Head to heels, your baby now measures about 13 1/2 inches. His weight — a pound and a half — doesn't sound like much, but he's beginning to exchange his long, lean look for some baby fat. As he does, his wrinkled skin will begin to smooth out and he'll start to look more and more like a newborn. His hair is probably recognizable now (in color and texture), although both may change after he's born.

WEEK 26 

Your baby now weighs a little under 2 pounds and measures about 14 inches, from head to heel. The nerve pathways in her ears are developing, which means her response to sounds is growing more consistent. Her lungs are developing now, too, as she continues to take small breaths of amniotic fluid — good practice for when she's born and takes that first breath of air. If you're having a boy, his testicles are beginning to descend into his scrotum — a trip that will take about two to three days.

WEEK 27 

Your baby is really starting to fill up your uterus. This week he weighs almost 2 pounds and is about 14.4 inches long with his legs extended. He can now open and close his eyes, and he sleeps and wakes at regular intervals. He may suck his fingers, and although his lungs are still immature, they would be capable of functioning — with assistance — if he were to be born prematurely. Chalk up any rhythmic movement you may be feeling to a case of baby hiccups, which may be common from now on. Each episode usually lasts only a few moments, and isn't bothersome to him, so enjoy the tickle. With more brain tissue developing, your baby's brain is very active now. Wonder what he's thinking?

WEEK 28 

By this week, your baby weighs a little over 2 pounds and measures about 14.8 inches from the top of her head to her heels. She can open her eyes — which now sport lashes — and she'll turn her head toward a continuous, bright light from the outside. Her fat layers are beginning to form, too, as she gets ready for life outside the womb.

WEEK 29 

Your baby now weighs about 2 1/2 pounds and is a tad over 15 inches long from head to heel. His muscles and lungs are continuing to mature, and his head is growing bigger to accommodate his brain — which is busy developing billions of neurons. With this rapid growth, it's no surprise that your baby's nutritional needs reach their peak during this trimester. To keep yourself and him well nourished, you'll need plenty of protein, vitamin C, folic acid, iron, and calcium. (About 200 milligrams of calcium is deposited in your baby's skeleton — which is now hardening — every day.)

WEEK 30 

Your baby's a bit more than 15 1/2 inches long now, and she weighs almost 3 pounds. A pint and a half of amniotic fluid surrounds her, but that volume will decrease as she gets bigger and fills out your uterus. Her eyes open and close, she's able to distinguish between light and dark, and she can even follow a light source back and forth. Once she's born, she'll keep her eyes closed for a good part of the day. When she does open them, she'll respond to changes in light but will have a visual acuity of only 20/400 — which means she can only make out objects a few inches from her face. ("Normal" vision in adults is 20/20.)

WEEK 31 

This week, your baby measures about 16 inches long. He weighs a little over 3 pounds and is headed for a growth spurt. He can turn his head from side to side, and he's beginning to accumulate a layer of fat underneath his skin in preparation for life as a newborn. As a result, his arms, legs, and body are filling out.

WEEK 32 

By now, your baby probably weighs almost 4 pounds and is almost 17 inches long, taking up a lot of space in your uterus. She has tiny toenails now, and her fingernails have grown in, too. Some babies have a head of hair already; others have only peach fuzz.

WEEK 33 

This week your baby weighs a little over 4 pounds and measures 17.2 inches from the top of his head to his heels. His skin is becoming less red and wrinkled, and while most of his bones are hardening, his skull is quite pliable and not completely joined. This will help him ease out of your relatively narrow birth canal.

WEEK 34 

Your baby now weighs about 4 3/4 pounds and is probably almost 18 inches long. Her fat layers — which she'll need to regulate her body temperature once she's born — are filling her out, making her rounder. Her central nervous system is still maturing and her lungs are well developed by now. If you've been nervous about going into preterm labor, you'll be happy to know that 99 percent of babies this age can survive outside the womb — and most have no major long-term problems related to prematurity.

WEEK 35 

Your baby's getting big. He weighs a tad over 5 pounds and is just over 18 inches long. Because it's so snug in your womb, he isn't likely to be doing somersaults anymore, but the number of times he kicks should remain about the same. His kidneys are fully developed now, and his liver can process some waste products. Most of his basic physical development is now complete — he'll spend the next few weeks putting on weight.

WEEK 36 

Your baby is still putting on the pounds — about an ounce a day. She now weighs almost 6 pounds and is a little less than 19 inches long. She's shedding most of the downy covering of hair that covered her body as well as the vernix caseosa, the creamy substance that covered and protected her skin during its submersion in amniotic fluid. Your baby swallows both of these substances, along with other secretions, which will stay in her bowels until birth. This blackish mixture, called meconium, will become her first bowel movement.

At the end of this week, your baby will be considered full-term. (Babies between 37 and 42 weeks are considered full-term; a baby born before 37 weeks is pre-term and after 42 is post-term.) Most likely she's in a head-down position by now, which is optimal for a smooth delivery, but if she isn't in the next week, your provider may suggest scheduling an "external cephalic version," which is a fancy way of saying she'll try to coax your baby into a head-down position manually, by manipulating her from the outside of your belly.

WEEK 37 

Congratulations! Your pregnancy is now considered full term — meaning your baby is developmentally ready to handle life outside the womb. (Babies born before 37 weeks are pre-term and those born after 42 weeks are post-term.) Your baby probably weighs a little over 6 pounds at this point and measures between 19 and 20 inches, head to heel.

Many babies have a full head of hair at birth, with locks from 1/2 inch to 1 1/2 inches long. But don't be surprised if your baby's hair isn't the same color as yours. Dark-haired couples are sometimes thrown for a loop when their children are born blonds or redheads, and fair-haired couples have been surprised by Elvis look-alikes. And then, of course, some babies sport only peach fuzz.

WEEK 38 

Your baby has really fattened up. She likely weighs between 6 and 7 1/2 pounds now (boys tend to be slightly heavier than girls), and she's probably between 19 and 20 inches long. She has a firm grasp, which you'll soon be able to test with your pinky! Her organs are fully developed and in place, but her lungs and brain — though developed enough for her to function now — will continue to mature right through childhood.

Wondering what color your baby's eyes will be? You may not be able to tell right away. If your baby is born with brown eyes, they'll likely stay brown. If she's born with steel gray or dark blue eyes, they may stay gray or blue or turn green, hazel, or brown by the time she's 9 months old. That's because a child's irises (the colored part of the eye) may gain more pigment in the months after she's born, but they won't get "lighter" or more blue. (Green, hazel, and brown eyes have more pigment than gray or blue eyes.)

WEEK 39 

Your baby's ready to greet the world! He continues to build a layer of fat to help control his body temperature after birth, but it's likely he already measures about 20 inches and weighs a bit over 7 pounds. (Boys tend to be slightly heavier than girls.) Your baby's organs are fully developed and in place, and the outer layers of skin are sloughing off as new skin forms underneath.

WEEK 40 

It's hard to say for sure how big your baby will be, but the average newborn weighs in at a little over 7 pounds and is about 20 inches long. Your baby will continue to grow with every passing day (her nails and hair will continue to get longer, too). Your baby's skull bones are still separated and they'll stay that way to allow the bones to compress enough to fit through the birth canal during labor (you'll notice soft spots or "fontanels" on your baby's head for a year or more after birth).

WEEK 41 

A bit over 20 inches long, your baby has continued to grow and may now weigh almost 8 pounds. As cozy as he is, your baby can't stay inside you forever. For your baby's safety, your practitioner will talk with you about inducing labor if your baby isn't born in the next week — earlier if there are any problems. Most practitioners won't let you wait more than two weeks past your due date to give birth because it puts you and your baby at increased risk for complications. About 5 to 6 percent of women have prolonged pregnancies that extend three or more weeks beyond their estimated due dates. Babies born at 42 weeks and beyond can have dry parchment-like skin and are often overweight. Waiting that long to deliver also increases your chance of developing an infection in your uterus that could be dangerous for your baby or of having a stillbirth. What's more, your labor is more likely to be prolonged or stalled, both you and your baby have an increased risk of injury during a vaginal delivery, and you double your chances of needing a c-section.

YOUR NEWBORN 

Because he was curled up inside your uterus until recently, your newborn baby will probably look scrunched up for a while, with his arms and legs not fully extended. He may even appear bowlegged.

Don't worry: Your baby will stretch out, little by little, and by the time he reaches 6 months, he'll be fully unfurled! In the meantime, as he adjusts to life outside the warm, safe confines of your womb, he may enjoy being swaddled in a light blanket.