Baby Growth

Week 01 to Week 04

Week 1

This week, you would have your last menstrual periods before you conceive. That means, your expected delivery date is calculated as 40 weeks from the first day of last menstrual period and this week is considered as part of your pregnancy period. Your oestrogen hormone levels increase and a special kind of mucous like substance lines your uterus and the fallopian tubes to facilitate transit of sperms into the tubes. This mucous also protects and keeps the sperms alive for about 3-5 days. While you plan to conceive, prepare yourself well. Avoid alcohol, drugs, tobacco or any other substances that are harmful to your baby. Eat a healthy diet rich in vitamins, particularly folic acid.

Week 2

You would have released an ovum (egg) around this time and if viable sperms remain in the fallopian tube, fertilisation of the egg by the sperm may take place close to end of this week. You would have conceived and a new life starts growing within you!

Week 3

During these seven days after conception, the fertilised egg undergoes a series of cell division beginning from breakdown into two cells, then four followed by eight cells and then goes on dividing as it travels from the fallopian tube into your uterus (womb). Once in the womb, this group of cells appears like a small ball (morula). This ball of cells becomes fluid-filled (blastocyst) and towards the end of this week, blastocyst gets embedded into the lining of your womb. This is called implantation process and takes about six days to be completed. Once implanted, the developing embryo can access your blood supply and receive nutrition. Your baby starts producing a hormone called human chorionic gonadotropin (HCG), which prevents your menstrual periods and turns your pregnancy test positive.

Week 4

Your baby which is a ball of cells just about the size of an apple seed is now called an embryo. It is made of 2 cell layers called epiblast and hypoblast which form future organs and tissues of the baby. Amnion and the yolk sac are two other structures that develop this week. The amnion with its amniotic fluid envelops and protects the growing embryo. Yolk sac makes the blood that nourishes the embryo until placenta forms and takes over the function.

Week 05 to Week 07

Week 5

Week 5

Your baby that looked like a mass of cells until now, gains a distinct shape this week. The embryo is about half a centimetre long and appears as a tadpole. The neural tube develops which will later become your baby’s spinal cord and brain. Your baby’s heart and other vital organs such as kidneys and liver start developing. The placenta also forms this time and your baby gets nourishment from your blood through the placenta.

Week 6

Your baby has grown to about the size of a lentil by now. The brain and spinal cord are developing at a faster rate. Your baby has its facial features developing with those dark spots that transform into eyes and the pits on either side of the head make up the ear. Baby’s heart starts beating around this week and heart rate can even be detected on an ultrasound during your prenatal visit. Small buds protrude out that eventually form your baby’s hands and feet. The digestive and respiratory system organs start forming this week.

Week 7

Now onwards your baby almost the size of a grape enters a very active developmental stage and at the same time starts adapting to the life inside your womb. The umbilical cord which acts as a linkage between you and your baby throughout pregnancy has formed by now. This serves as a portal to provide oxygen and nutrition to your baby and also for waste disposal from baby’s body.

Your baby is growing at a rapid pace and all the body parts that have started forming in the earlier weeks (heart and brain) differentiate and become complex. Your baby’s digestive tract and lungs also continue to develop. At the end of the arm bud that had formed last week, a small hand which looks like a paddle appears. By this week, baby’s face acquires a distinct shape as facial features such as mouth, nostrils, ears and eyes become more defined.

Week 08 to Week 12

Week 8

Week 08 to Week 12

Your baby measures almost one and a half centimetre by this week. Lot of change takes place this week. The cute little fingers and toes which you long to cuddle with begin to form. Your baby can now bend its hand at the elbow and wrist. The eyes become more evident as they form pigment and also eyelids form to protect the eyes. The buds that develop into your baby’s genital organs also appear this week.

Week 9

Your baby now appears like a peapod and weighs around 2-3grams. By the end of this week, your baby will measure up to 2.3 centimetres in length. The tail like extension at the end of spinal cord disappears and baby’s head grows very large compared to the rest of the body. The hands have grown longer and fingers become clearly distinguishable. Baby’s genitals start to develop from the buds that had appeared in the previous week. Also, internal reproductive organs such as testes and ovaries begin forming this week. Your baby may make few of its first movements in this week which can be well appreciated on an ultrasound.

Week 10

By the end of this week, your baby has crossed the embryonic period and will be regarded as foetus from the next week onwards. The foetus measures 3 centimetres and weighs not more than just 4 grams. Your baby starts developing very fine details such as fingernails and hair as it grows each day. The vital organs –the heart, liver, kidneys, brain and lungs have formed completely and started their function. Tooth buds appear inside the mouth. If the foetus is male, then its testes begin producing testosterone, the male hormone.

Week 11

You are heading towards the end of the first trimester. Your baby starts active movements like kicking and stretching. Your baby’s fingers and toes have separated and the baby grows rapidly from now on until 20 weeks. The face continues to develop and the ears take their final location, on the sides of the head. Your baby’s head seems larger and is at least half the baby’s length.

Week 12

This week marks the end of your first trimester. Baby’s vocal cords form this week. Your baby’s kidneys start to function as the amniotic fluid your baby swallows is passed out in the form of urine. The eyes which were on the side of the head come closer together. Brain development continues and by the end of this week, your baby may become about 5.5 centimetre long and weigh around 14 grams.

Week 13 to Week 15

Week 13

Week 13 to Week 15

You have stepped into the second trimester of your pregnancy. You have your fully developed placenta to provide your baby enough oxygen, nutrients and also dispose waste. Along with this, the placenta starts producing hormones, progesterone and oestrogen that maintain your pregnancy. Your baby’s eyelids get fused together in order to protect the developing eyes. Surprisingly, your baby’s unique fingerprints have also developed by this time. Your baby measures around 7 to 8 centimetres long and weighs about 23 grams.

Week 14

During this week, very fine colourless hair develops and covers most of the baby’s body. It is called lanugo and it usually disappears just before birth. Eyebrows also start growing as do the hair on the scalp. Your baby’s genitals have also completed development. Your baby can make expressions –squint, frown or grimace and is able to grasp and suck its thumb. By now your baby’s body starts growing faster than the head portion and measures about 9 centimetre in length and weighs around 43 grams.

Week 15

Your baby is now about 15 centimetres in length head to toe and may weigh around 120 grams by the end of this week. The head portion may account for almost 1/3 rd of the baby’s body length. If you have been pregnant before, you may start feeling sensations of your baby’s movements in this week. Your baby is able to make some facial expressions and has the ability of grasping with hands and sucking the thumb. Your baby may start exploring inside your womb with its little hands! Baby’s vocal chords have also formed by now. The amount of amniotic fluid surrounding your baby also increases allowing it to move around freely in the womb. Hair continues growing on the head and eyebrows. The skeletal system and muscles continue developing due to which baby is able to move his arms and legs.

Week 16 to Week 18

Week 16

Week 16 to Week 18

Your baby has grown up to the size of a pear fruit and in the following weeks there will be rapid growth in your baby. Your baby is able to hold its head in an erect position and can make facial expressions such as squinting and frowning. Besides these activities, your baby may also catch hold of the umbilical cord and start playing with it! The circulatory system and urinary system are fully functional and your baby inhales and exhales the amniotic fluid through the lungs.

Week 17

Your baby may measure upto 19 centimetres from the head to toe and weigh almost 280 grams by the end of this week. Baby’s skin appears transparent and wrinkled as the fat layer underneath has not developed yet. The blood vessels beneath the skin can be seen and makes the skin appear purple-red. A fine layer of hair called lanugo covers your baby’s body and protects the tender baby skin until it is shed a few weeks before birth. Your baby begins exploring its own body with the hands and there is ample amount of amniotic fluid for the baby to swim around and shift position very often.

Week 18

An ultrasound scan is usually done between 18 and 20 weeks during which you may see your baby kick, move arms or even suck the thumb. Your baby’s chest moves up and down when it inhales and exhales amniotic fluid, in a similar way as while breathing. The ears take their final position and in following weeks your baby may listen to your voice! The middle ear bones and nerves from the brain have developed and your baby can make out sounds of blood gushing through the umbilical cord and your heartbeat. Your baby’s bones which have been soft till now start to harden or ossify during this week.

Week 19 to Week 22

Week 19

Week 19 to Week 22

By the end of this week, your baby may measure about 22 centimetre head to toe and weigh around 340 grams. Your baby’s fingernails have completely formed and fingerprints can be seen engraved in their thin skin. Permanent tooth buds appear behind the primary tooth buds deep within the gums. A waxy layer called vernix caseosa covers and protects your baby’s subtle skin from harm.

Week 20

You have completed almost half of your journey through pregnancy this week! Your baby grows rapidly taking up more space in the womb. As your baby continues growing, you can feel more pressure on your lungs, stomach and bladder. Your baby’s skin develops into layers and becomes thicker below the vernix caseosa. Hairs and nails keep growing.

Week 21

Your baby will be measuring around 25 centimetres from head to toe and weighing slightly less than half a kilogram by this week. Baby’s eyelids remain fused but the retina of the eye has formed completely. Eyelashes and eyebrows have formed. The hair follicles develop pigments that give your baby’s hair its colour. At this stage, your baby lies in a crossed position with feet towards one side of your stomach and head on the other side. Bone marrow has now developed well enough to take over the production of blood cells from the baby’s liver and spleen.

Week 22

Your baby looks more proportional and weighs around 430 grams and nearly 27 centimetres from head to toe. The first tooth buds have appeared in the baby’s gums. By the end of 22 weeks, baby’s nervous system develops completely and the connection between brain and spinal cord matures. Your baby is now able to recognise light, sound and feeling of touch, warmth and pain. Taste buds have begun forming on the tongue. Baby’s reproductive system also continues developing. The testes start descending from the abdomen if it is a baby boy and in girls’ uterus, ovaries and vagina would have developed.

Week 23 to Week 25

Week 23

Week 23 to Week 25

You may observe that your baby tends to be more active this week, particularly during the time when you are resting. The baby adopts a distinct pattern of sleep though they sleep for most of the time. By now, your baby may measure up to 28 centimetres and weigh approximately 600 grams. A fat layer starts forming in between the muscles and skin and covers the blood vessels giving a better skin complexion.

Week 24

At 24 weeks, babies will have increased breathing patterns. A substance called surfactant is produced in the baby’s lungs and lines the lungs to help the baby breathe after it is born. Your baby may weigh more than 600 grams by now and measure up to 30 centimetres in length. Baby’s skin is very thin and delicate and has very little amount of body fat.

Week 25

Your baby can now hear and recognise your voice and be calmed by listening to various types of music. Eyelids can open; your baby can even blink and react to bright light. Your baby is about 33 centimetres in length and may weigh about 800 grams. Baby’s movements become more regular and you may observe baby has resting and active periods.

Week 26 to Week 28

Week 26

Week 26 to Week 28

Your baby’ skin may be wrinkled though the body weight is about 907 grams. Baby will steadily gain weight in the following 14 weeks. As the nerves in the ear have developed completely, response to sound becomes more consistent. Baby’s brain also develops intensely as baby grows at a rapid rate. Your baby continues to take small breaths of fluid surrounding it.

Week 27

In the 27th week of pregnancy, your baby weighs about 1100 grams and measures 37 centimetres. Immune system develops in your baby as your natural antibodies pass into the baby through the placenta. Your baby is now able to coordinate the ‘suck and swallow’ action which is essential for feeding after birth. The ability to distinguish light from dark also develops by now. Your baby will almost appear the way she is going to look at birth except that she is thinner and smaller.

Week 28

By the end of week 28, your baby may measure about 38 centimetres from head to toe and weigh slightly over 1000 grams. In this week your baby can open its eyes and turn head towards a continuous bright source of light from outside. The layers of fat continue to deposit and hair growth also continues. The baby’s brain folds and grooves also develop and expand.

Week 29 to Week 33

Week 29

Week 29 to Week 33

The third trimester begins from the 29th week and lasts till birth that is around 40 weeks. Your baby weighs about 1350 grams and may be around 40 centimetre in length. Baby’s brain increases in size and becomes more complex. The pupils in the baby’s eyes can react to light and your baby can focus without much difficulty and view dim shapes. Your baby’s movements continue to be more active and in case you notice decrease in movements, consult your doctor.

Week 30

Your baby will continue gaining weight rather than growing in length from now onwards. Your baby may weigh around 1400 grams and continue depositing fat layers to gain weight. A special kind of fat called brown adipose tissue gets deposited which helps to regulate newborn infant’s body temperature and serves as important source of heat production after birth. About 1 litre of amniotic fluid may surround your baby now, but its level decreases as baby grows. Your baby’s lungs are fully developed and baby may repeatedly move the diaphragm imitating breathing movements. Your baby may also get hiccoughs which are felt as rhythmic jerky motion within your womb.

Week 31

Your baby now weighs around 1700 grams and looks slightly chubby. The head to toe length of the baby would be about 43 centimetres. Your baby’s lungs produce more and more amounts of surfactant, a fatty liquid that keeps the lining of the lungs moist and efficient enough for breathing. The ‘suck and swallow’ action necessary for the baby to feed after birth gets fully coordinated by the end of this week. Your baby may swallow some amount of amniotic fluid and also pass several cups of ‘urine’ through bladder back into the amniotic fluid around it. You may feel your baby does not make as many movements as before, but this is because of lack of space in the womb as baby grows bigger.

Week 32

Your baby will have hair on the head, eyelashes and eyebrows evident by now. The fine hair that had covered baby’s body from the second trimester disappears, but some hairs may persist at birth on the back and shoulders. Your baby keeps practising breathing movements by inhaling amniotic fluid and exercising the lungs! If you are carrying a baby boy, his testicles descend from the abdomen into the scrotum.

Week 33

Your baby will turn around and be in a ‘head down’ position until birth. Baby’s movements may change into stretches and twists as it grows bigger and there is relatively less space to move around in the womb. Your baby will weigh about 2100 grams and measure approximately 45 centimetres in length. During the remaining 6 weeks, the main task for your baby is to grow bigger by gaining weight and to boost the immune system with your antibodies. Now, your baby’s brain has billions of well developed nerve cells which help your baby coordinate with the in utero environment by senses of hearing, sight and touch. Your baby will be able to distinguish different flavours, whether sweet or sour! Your baby is at sleep most of the times and may even experience dreams!

Week 34 to Week 36

Week 34

Week 13

At 34 weeks, fat layers continue to deposit and your baby weighs around 2200 grams by now. Your baby’s nervous system continues to mature and the lungs are almost fully developed. You can even talk to your baby as the hearing ability is fully developed. The fine hair (lanugo) has fallen off but the waxy covering on your baby’s skin, vernix caseosa becomes thicker.

Week 35

Your baby’s expected delivery date is fast approaching and your baby is now in normal proportion and plump! Your baby could weigh around 2600 grams and measure upto 47 centimetres head to toe by this week. Now onwards the overall growth of your baby becomes slow but weight gain increases considerably to up to approximately 230 grams per week. From this week, the most rapid weight gain period begins and fat deposits throughout baby’s body particularly around shoulders.

Week 36

Your pregnancy completes full-term by the end of this week and you could give birth to your baby any time from now! Your baby may weigh about 2700 grams and you may feel increasing pressure in the lower part of your abdomen. Your baby’s cheeks become chubbier which adds to the fullness of your baby’s face. While your baby’s head is in the pelvis, the skull bones may also move in relation to one another (molding). It facilitates easy passage of your baby through birth canal.

Week 37 to Week 40

Week 37

Week 37 to Week 40

Your baby may weigh about 3000 grams and measure almost 48.5 centimetres head to toe length. Your baby is regarded as ‘full term’ or being on time if born after this week. The thick white layer on baby’s skin (vernix) remains, but the fine hair covering the body, lanugo would have disappeared by this week. However, fat continues depositing at the rate of 14 grams a day!

Week 38

You are just two week away of holding your little one in your hands! Though baby’s growth has slowed down, fat still accumulates. Waste substances begin collecting in the baby’s intestines. Dead skin cells, intestinal cells and lanugo hair pile up to form the greenish-black meconium, baby’s first bowel movement.

Week 39

Nearly all of the vernix coated on the baby’s skin has disappeared but there may be some remaining in the armpits or groin areas. Your baby’s breathing exercises usually stop about 24-48 hours prior to commencement of the labour. About 75-100 ml of amniotic fluid remains in the baby’s lungs and hormones released during labour initiates absorption of fluid from the lungs into the blood stream. Umbilical cord may become entangled around baby’s neck sometimes, in this case a Caesarean section would be required if it causes problems.

Week 40

After much of expectations and preparation, you may welcome your baby this week. Your baby at term may weigh in the range of 2800 grams to 4500 grams and measure somewhere around 46 to 56 centimetres. Your newborn may have slight variations such as misshapen head, vernix coating, skin discolourations, dry patches or rashes. All these are quite normal and will resolve in few days.

  • Monash Obstetrics
  • Ph: 1300 121 000
  • 15 Murray Street, Clayton, Victoria 3168
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