Pregnancy: Week by Week

Looking for a week-by-week guide to pregnancy? You're in luck!

Read on to learn more about what you can expect with you and your baby every week of your pregnancy. Your baby's changing day by day, and your body is keeping pace. Find out what's going on with this week-by-week pregnancy guide.

Week by Week

1Week 1 - The arrival of the fertilized egg
In the first Week of pregnancy there is no baby yet. For now, your uterus is preparing for the arrival of the fertilized egg, even though you can’t really tell for sure that the egg has successfully matched up with sperm until next month.
2Week 2 - The arrival of the fertilized egg
While it’s hard to calculate the exact moment pregnancy begins, your conception date is considered to be two Weeks before the first day of your next expected menstrual period. It really all comes down to the moment your egg meets the sperm.
3Week 3 - Conception and fertilization
This Week you definitely ovulated, so the zygote starts its remarkable journey to a baby boy or girl! Within days it will divide into two cells, then four and so on, until the cluster will comprise around 100 cells. Some of the cells form the embryo, others the placenta. As it divides, the blastocyst starts traveling to your uterus a journey where it will implant itself in the uterine wall and grow for the next nine months. Your baby's appearance, sex and other characteristics are determined at fertilization.
4Week 4 - Placenta and embryo are developing
Your embryo is no longer than one millimetre and no bigger than a poppy seed, but is busy developing at an incredible fast pace. Your embryo splits into two parts this Week: half of it will become your son or daughter, while the other half forms the placenta, the lifeline that channels nutrients to your baby and carries waste away until delivery. The embryo has now three different layers of cells that will grow into specialised parts of your baby's body.
5Week 5 - Baby’s heartbeats beat for the first time
Your baby is now the size of an orange seed, at least twice as big as before. Your pregnancy hormone levels are now high enough to confirm that you are expecting using a home pregnancy test. One of the first systems to be operational in your baby’s developing body is the circulatory system and of course, the heart. When you are 5 Weeks pregnant, your baby’s heart is made up of two small channels called heart tubes and they are already strong at work.
6Week 6 - Baby's head takes shape
Your baby is now the size of the length of a sweet pea, measuring anywhere from 5 to 6mm. For the first time, your baby's jaw, cheeks and chin are now visible. All those little indentations on both sides of the head are in fact the developing ear canals. Small bumps on the face will form the eyes and button nose in a few Weeks time. Also taking shape this Week are the baby’s kidneys, liver and lungs, along with the heart, which is now beating 80 times a minute, and is usually visible on ultrasound.
7Week 7 - Baby's arms and legs are developing
Your baby's approximately 7mm in length now, about the size of a blueberry. At 7 Weeks pregnant, most of that growth is concentrated in the head as new brain cells are generated at the rate of 100 per minute. Also, baby’s arm and leg buds begin to sprout and expand into hand, arm and shoulder segments and leg, knee and foot segments. Also forming this Week are your baby's mouth and tongue. At this stage, even though your embryo is just one month old, it's already gone through three sets of kidneys.
8Week 8 - Baby's Facial features are visible
At a length of about 10mm, your baby is the about the size of a raspberry and is growing at a rapid rate, a millimetre every day. You are able to see now an upper lip forming, the tip of the nose and tiny, thin eyelids. Also, his or her heart is beating at the incredible rate of 150 times per minute, about twice as fast as the adult heart beats. And even though you can't yet feel it, baby is making spontaneous movements as he or she twitches the trunk and limb buds.
9Week 9 - The start of the fetal period
Your foetus is now about 25mm long, the size of a cherry. Your little one is getting bigger every day, the head is about the same size as the rest of his or her body. The ears are much more prominent and some new organs liver, spleen and gallbladder are forming. Your foetus is also making spontaneous movements of his or her arms and legs now that micro muscles are beginning to develop.
10Week 10 - Baby's bones are hardening
Your baby is nearly 35mm long, the size of a prune. In fact, your baby went from an embryo to a full-developed foetus. Bones and cartilage are forming and the knees and ankles are shaping. The arms (complete with elbows) can flex already. The baby’s teeth are now beginning to form under the gums. Your baby's stomach is producing digestive juices, the kidneys are producing larger quantities of urine and, if your baby's a boy, he's already producing testosterone.
11Week 11 - Fingers and toes are emerging
Your baby is the size of a brussels sprout, 5cm. By Week 11 of pregnancy, baby has distinct human characteristics: hands and feet, ears in their final shape, open nasal passages on the tip of the nose, a tongue and palate in the mouth and visible nipples. The head is currently equal in length to the rest of the body and hair follicles are forming on the crown. The hands and feet have individual fingers and toes and by next Week, the nails themselves will start to grow.
12Week 12 - Digestive system is at work
Your baby weighs 15g, with a crown-to-rump length of about 6.5cm, about the size of a large plum. Your baby’s systems continue to mature for the next 28 Weeks. For one thing, the digestive system is beginning to flex its digestive muscle as it produces contractions. The great news is that in this stage you will often hear your baby's first heartbeats.
13Week 13 - Second trimester begins
Your baby is as large as a peach and is now about half the size of her crown-to-rump length. In this stage, babies begin growing at different paces. Also, tiny bones are beginning to form in her arms and legs. Your baby's intestines are also in for some big changes, moving towards his/her abdomen. And to serve your growing baby's needs, the placenta is also growing. Also developing this Week are the vocal cords. Because sound can't travel through your uterus, you won't be able to hear any sounds or cries just yet.
14Week 14 - It’s all about hair now
Now the size of a small apple, your baby is constantly moving, his or her neck is getting longer and stronger, making the head stand more upright. Baby's first ultra fine, downy hair, is now covering his back, shoulders, ears, and forehead. It helps him or her retain body heat, but once he gains enough fat, this hair will fall after birth. If you are having a boy, the prostate begins to develop, and if you are having a girl, her ovaries are moving down into her pelvis.
15Week 15 - Constantly kicking and flexing
Your baby is the size of an avocado. Babies practice breathing, sucking and swallowing and other skills necessary for survival. Your little one is constantly kicking, curling toes and moving those little arms and legs but you won't be able to feel the movements just yet. Also, facial expressions are your baby's latest tricks, he is now learning to flex all of his or her facial muscles, frowning, squinting, grimacing and wincing. By now, the ears are positioned properly on the sides of the head and the eyes are moving from the side of the head to the front of the face.
16Week 16 - Baby can hear your voice
Your baby is now the size of an orange, weighing 100-125g and he or she is 10-12cm in length. Baby’s eyes are making side-to-side movements and perceive light, even though the eyelids are still sealed. Tiny bones in your baby’s ears are fully formed, making it likely that your son or daughter can hear your voice at 16 Weeks pregnant. In fact, studies have shown that babies who hear a song while they are in the womb will recognise it after they are born.
17Week 17 - Practicing more sucking and swallowing
Your baby weighs about 100g and is about the size of your palm. The heart is now regulated by the brain to beat 140 to 150 times per minute and fat stores that will keep the baby warm are now beginning to develop, Baby is also making great progress at sucking and swallowing in preparation for suckle at your breast or bottle. Within the next Week, your baby's unique fingerprints will take shape. As your baby’s hearing is fully developed, loud noises will actually startle your baby and also get him or her used to such sounds.
18Week 18 - Feeling your baby kicking and punching
Your baby is about the size of a soda can, 14cm long and 140g in weight. Baby is big enough now for you to feel him stretching and rolling his way around the womb. Yawning is your baby’s latest trick and also your baby's nervous system is maturing at a fast pace. Nerves, now covered with a substance called myelin (which speeds messages from nerve cell to nerve cell), are forming more complex connections. Cells in the brain are specializing into the ones that serve the senses of touch, taste, smell, sight and hearing.
19Week 19 - Baby has a protective coating
Your baby is now the size of a large tomato, 15cm and about 225g in weight. Arms and legs are finally in proportion, neurons are now connected between the brain and muscles and cartilage throughout the body is turning to bone. All these upgrades combine to give your baby more control over limb movements. Your baby is getting a protective substance that will keep your baby's sensitive skin safe from the surrounding amniotic fluid. Without it, your baby would look very wrinkled at birth.
20Week 20 - Girl or boy?
Your baby is the size of a mango and weighs about 275g and has a height of about 16.5cm. Even though baby’s external genitals are still developing, you will be able to find out your baby's gender via the second trimester ultrasound scheduled for anytime between 18 and 22 Weeks. For some babies this might be the Week when their eyelids are opening for the first time. And as baby’s hair, nails and eyebrows continue to sprout, your child is looking more and more like his or her parents.
21Week 21 - Baby gets taste buds
About the size of a large banana, 17.5 in length and almost 325g in weight, your baby sleeps as much as a newborn, perhaps 12 to 14 hours per day. At 21 Weeks pregnant, your baby swallows a bit of amniotic fluid each day, not only for nutrition and hydration, but also to practice swallowing and digesting. The taste of the amniotic fluid differs from day to day depending on what the mother is eating. Experiments show that babies who were exposed to certain tastes in utero via the amniotic fluid were more eager to eat foods with that same taste after birth.
22Week 22 - Sharpening all the senses
At half a kilogram and 20cm, your baby is about the size of a papaya. Baby’s lungs are developing rapidly, and they will begin making a protein called surfactant, which will help her or him breathe independently after birth. Eyelashes and eyebrows are also well formed now and more hair is sprouting atop the head. However, at this stage the hair has no pigment, so it's bright white. Other senses are getting more and more developed: touching, seeing, hearing. Baby's ears begin to hear and process sounds from inside mother’s body: breathing, heartbeats.
23Week 23 - Serious baby weight gain
Your baby is as big as an eggplant. At 20cm and 500g, this Week marks the beginning of some serious weight gain. Your baby should double the weight over the next four Weeks. A thick, protective protein called keratin is being added to baby's skin cells, helping his or her skin to thicken. Also, baby's skin displays a red hue thanks to the developing veins and arteries right underneath. At this stage you will be able to hear baby’s heartbeat through a standard stethoscope.
24Week 24 - Baby’s face is formed
Your baby is as long as an ear of corn, about 22cm long and weighs 700g, gaining steadily at a rate of about 150g per Week. Much of that weight comes from growing organs, bones, muscle and accumulating baby fat. Baby’s tiny face is almost fully formed, complete with eyelashes, eyebrows and hair. All of the hair is white since there is no pigment yet. Also, baby’s nostrils are beginning to open for 'practicing breathing' and she or he will through the same patterns of real breathing but inhale amniotic fluid instead of air.
25Week 25 - Baby’s lungs closer to maturity
Your baby is the size of an acorn squash, 23cm in length and passing the 750g mark. Later this Week, blood vessels will also develop in your baby's lungs, bringing them one step closer to full maturity. But at 25 Weeks pregnant, those lungs are still working to mature. Though they are already beginning to develop surfactant, a substance that will help them expand with oxygen after the baby is born, the lungs are still too undeveloped to sufficiently send oxygen to the bloodstream and release carbon dioxide when baby exhales.
26Week 26 - Baby’s eyes are opening
Your baby is the size of a turnip and weighs 900g and measures 24cm. Your baby's eyes have been closed for the past few months but are now beginning to open at 26 Weeks pregnant and your baby is able to see inside the uterus. Right now the iris, the coloured part of the eye, still doesn't have much pigmentation.Your baby's brain-wave activity is progressing fast at this stage of development, which means your little one can not only hear sound but can now also respond to them with an increase in pulse rate or activity.
27 Week 27 - Huge growth spurt
Your baby is the size of an eggplant, your baby is now measuring nearly 35cm and weighs nearly 1kg. This Week alone your baby will grow a massive 3cm. Your little one is able to recognize familiar voices by now. His or her hearing is progressing as the network of nerves to the ears matures, though the sounds are muffled thanks to the coating of vernix covering those ears. Your baby's taste buds are very developed now as well, and although hiccups which may feel like belly spasms for the mother are quite frequent, the baby isn't bothered at all by them.
28Week 28 - Baby may be dreaming too
Your baby is the size of a cucumber, just over 1kg and almost 40cm long. Your little one is settling into the proper position for birth, with his head facing downward, though he may still move around a lot. He's busy these days blinking, coughing, more intense sucking, hiccupping and, perhaps most important, better breathing. Your baby may as well be dreaming as brain wave activity measurements indicates different sleep cycles, including the rapid eye movement phase, the stage when dreaming occurs.
29Week 29 - Permanent teeth are forming
Your baby is the size of a head of cauliflower, weighs 1.3kg now and measures about 42cm. In fact, over the next 11 Weeks, baby will double or even triple her or his weight. As more fat is deposited under the skin surface, her wrinkled skin is smoothing out. Also, the buds of your baby’s future permanent teeth begin to form in her or his gums now. Baby’s adrenal glands begin producing the hormones androgen and estrogen, which stimulate the mother body’s milk production.
30Week 30 - Brain is growing bigger
Your baby is the size of a small cabbage he/she is now weighing in at 1.4kg. Until now, the surface of your baby's brain was smooth but now it begins to wrinkle (the wrinkles are called convolutions) so that it can hold more brain cells. Now that baby’s brain and new fat cells are regulating his body temperature, the lanugo, the hair covering your baby's body is beginning to disappear. Your baby's bone marrow has taken over production of red blood cells and now he or she will be more able to thrive on his or her own once born.
31Week 31 - Baby’s sense are really developed
Your baby is about as long as a bunch of leeks, weighing in at 1.5kg and measuring 45cm long, he is quickly approaching his birth length. The brain is working overtime developing faster than ever and making connections between individual nerve cells at a super-fast rate. Your baby is now processing information, tracking light and perceiving signals from all five senses. Of course he or she can't smell anything right now, but that's only because he's still submerged in amniotic fluid and needs to be breathing air to get a whiff of anything.
32Week 32 - Head down or breach?
Your baby is the size of a coconut, almost 1.7kg and just about 48cm. In these past few Weeks. All of your baby’s major organs are fully developed now, except for the lungs. These days it's all about practicing all the survival skills: swallowing, breathing, kicking and sucking. Anticipating mouth feeding, your baby’s digestive system is all formed. The skin is becoming less transparent and more opaque as more and more fat accumulates under the skin. There’s a chance baby has settled into the head-down, bottoms-up position in preparation for birth.
33Week 33 - Immune system is developing
Baby is the size of a head of lettuce, may be anywhere between 47 and 50cm in length and could grow up to another full 2cm this Week. The child weighs about 2kg and is still gaining weight, about 225g a week. The amniotic-fluid level has maxed out at by now, making it likely you have more baby than fluid now. Baby’s got her/his own immune system. Antibodies are being passed from you to your little one as he or she continues to develop the immune system, which will help the baby fight off all sorts of germs outside the womb.
34Week 34 - Baby’s got fingernails
Your baby is the size of a honeydew, he or she weighs 2.2kg and could be as tall as 50cm. If your baby is a boy, then you will be pleased to know that this Week his testicles are making their way down from his abdomen to his scrotum. In other baby-related developments, the fingernails have probably reached the tips of the fingers by now. Braxton-Hicks contractions can be felt from early on in your pregnancy. If these irregular, painless contractions increase later in your pregnancy they are also considered to be false labour rather than real labour.
35Week 35 - Significant gain weight
About the size of a honeydew melon, your baby is now over 45cm long and is approximately 2.3kg. Baby's kidneys are fully developed now, and the liver can process waste products. Most of his basic physical developments are now complete and she/he will spend the next few Weeks putting on weight. Fortunately the baby's skull remains soft. And for good reason: it will allow your baby to squeeze more easily through the birth canal. With less space in uterus now, the baby movements have shifted from kicks and punches to rolls and wiggles.
36Week 36 - Growth slows down
Baby is now about 2.7kg and 50cm long. Growth will experience a slowdown now. Baby's skull isn't the only soft structure in his or her little body. Most of your baby's bones and cartilage are quite soft as well. Many of your baby's systems are pretty mature, at least in baby terms and just about ready for life on the outside. Blood circulation, for instance, has been perfected and your baby's immune system has matured enough to protect him or her from infections outside the womb. Other systems, however, still need a few finishing touches.
37Week 37 - Practising for birth
Baby is the size of a large cantaloupe, he or she weighs about 2.9kg. Right now, your baby is busy rehearsing for his big meeting, simulating breathing by inhaling and exhaling amniotic fluid, sucking on his or her thumb, blinking and pivoting from side to side.Your baby's head will at birth, be the same size circumference as his or her hips, abdomen and shoulders. Baby is running out of room in the uterus, so he or she mostly stretches and wiggles, instead of kicking.
38Week 38 - Almost ready to go
Baby is the size of a winter melon, weighing 3.2kg and measuring 52cm long. Only two more Weeks, or longer, before your baby makes steps into your world. Your baby’s lungs have strengthened and his vocal chords have developed, which means he’s ready to communicate through wails and cries. The lungs will continue to mature and produce surfactant, a substance that prevents the air sacs in his lungs from sticking to one another once he starts to breathe.
39Week 39 - Baby’s skin becomes whiter
Your baby now weighs almost as much as a watermelon, by now your little one is officially considered a full-term baby. He or she weighs around 3-4kg and measures 48-52cm. At this point, baby has shed most of that white substance (vernix) and the fine hair (lanugo) that has covered their skin. Now, his or her skin has finally changed from pink thanks to a thicker fat layer has been deposited over the blood vessels. While their body isn’t growing as much, the brain is, it’s already 30 percent bigger than it was just 4 Weeks ago.
40Week 40 - Official end of the pregnancy
Now the size of a watermelon, your baby weighs anywhere from 2.8-4kg and measures between 48-53cm. Placenta is still providing the antibodies that he or she will need to fight off infections for the first six months of his life. Your baby’s major organs are ready for primetime and she/he will be letting you know soon when they are ready to meet you. Baby’s vision at birth is a bit blurry since she or he is only able to focus about an inch away, instead your baby will instantly recognise the sound of your voice and your partner’s.
41Week 41 - Stress hormones are good
Your baby is not considered overdue until 42 Weeks of pregnancy. Only 3 percent of babies arrive on their due date, about half enter into their tenth month of uterine life. During childbirth, your baby will produce more stress hormones than any other time in his or her life. These hormones will help your baby to adjust to life outside the womb and help all those survival instincts kick in. Also, first breath requires considerably more effort because the tiny air sacs in the lungs need to be inflated for the first time so that they expand fully to start breathing.
42Week 42 - Late delivery
Although it is perfectly normal for a baby to arrive past the due date, you and your baby will get some extra monitoring this Week. When the baby is ready to meet you, chances are the skin will be dry, cracked, peeling or wrinkled due to the protective vernix, which was shed Weeks ago in anticipation of a delivery. A tardy baby will also have longer nails, possibly longer hair and little or none of that lanugo. Since there's a chance your placenta may not provide as much oxygen and nutrients to your baby, your doctor might recommend inducing labour to be safe.

Do you have questions about your pregnancy?

Call Dr Christine Thevathasan

03 9500 9099