Your Unborn Baby’s Development - Week By Week Pregnancy

Your Unborn Baby’s Development

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Yes, once you start trying to conceive, or know that you are already pregnant, the journey ahead is going to be extremely breathtaking and breathless at the same time. Rest assured, there will never be a dull moment, and you’ll have plenty to look forward to.

And, you have much to look forward to in this new phase of life. But, the months ahead will see a tiny cell turn into your little darling. So, if you are trying to learn what your baby will look like at week 5 or week 23, you should consider reading our post.

Here, happy4thofjuly.us has the lowdown on what to expect, and how your how your baby will develop through each week of your ongoing pregnancy.

Your Unborn Baby’s Development Through Pregnancy Week By Week:

Here is how your baby will develop inside you through all the weeks of pregnancy:

1. At 4 Weeks:

  • At this stage, the embryo, which is, in reality, a ball of cells, is growing inside your uterus, or the womb. The embryo is the size of a poppy seed.
  • During the fourth week, the embryo divides into three different layers. The layers later turn into the various organs and tissues.
  • The neural tube begins to develop in the top layer. It will help develop the brain, backbone, spinal cord and your baby’s nerves later.
  • The middle layer will later develop into your baby’s heart and as well as the circulatory system.
  • The third layer houses your developing baby’s intestines and lungs, as well as the urinary system.
  • At this stage, your yolk sac begins to produce red blood cells, along with various nutrients that will help your baby. However, the initial role of the umbilical cord and the placenta will begin now and will soon start doing what the yolk sac does.
  • The cells of your placenta will now start to get rooted in the lining of your uterus. By the end of the fourth week, your placenta will start to function normally and will create the various nutrients that your baby needs.
  • It will also help remove your unborn baby’s waste products.
  • The umbilical cord helps carry nutrients and oxygen to your baby.

2. At 5 Weeks:

  • At this stage, your unborn baby’s heart will begin to divide into different chambers. Soon it will start to pump blood as well.
  • By now, your baby will measure about a quarter of a centimeter. Instead of looking like a human baby, your baby will look more like a tadpole at this stage, but don’t worry about it at all!
  • Sometime during this week, your baby will also begin exhibiting a growth pattern, one of the firsts in many to come soon.
  • Your baby’s major organs will steadily grow during this stage, including the liver and kidneys. The intestines will also develop while the appendix will position itself in place.
  • Sometime during this week, your baby’s neural tube, which was helping in connecting the brain and the spinal cord, will close up.
  • At this stage, your baby’s initial development of arms and legs will take place. Also, there will be small folds around the area that will later develop into your baby’s mouth. The folds will later make way to form your baby’s neck and lower jaw.

3. At 6 Weeks:

  • By now your baby will be approximately the size of a lentil.
  • Your baby’s heart will also start to beat at the rate of 150 beats per minute, which is almost double the rate at which your heart beats.
  • Your baby’s head will look bigger than the rest of the body.
  • By now, your baby’s first facial features begin to take shape. Dark spots appear where later the eyes will form, small openings will appear where the nostrils will form, and pits will appear to mark the area where the ears will appear.
  • Your baby’s arms and legs will look like buds that protrude from the cell mass. The muscle and bone tissues begin to develop, along with the pituitary gland which will release hormones later, and the rest of the brain.

4. At 7 Weeks:

  • Your baby will now be approximately 1.25 centimeter long, as big as a blueberry.
  • Your baby will now have slightly webbed fingers and toes and will start to move in sudden jerks.
  • At this stage, your baby’s liver will produce many red blood cells until the bone marrow develops and takes over the role.
  • Beginning now, until the end of the 20th week, your baby will experience a surge in development.
  • The body parts your baby developed earlier, will now become more prominent and specialized.
  • Your baby’s ears will keep developing, along with the teeth and palate.
  • At this stage, your unborn baby’s skin will be as transparent and thin as paper, and the veins will be visible throughout.

5. At 8 Weeks:

  • By now your baby will measure approximately 1.6 cm.
  • The tail that the embryo had until now begins to fade
  • All your baby’s organs begin functioning now, especially the different nerves and muscles.
  • The nerve cells in your baby’s brain will now start to branch out and connect with each other. It will be the first beginning in creating a neural pathway.
  • Your baby’s hand will now start to bend at the place where the wrist is, and the webbed look from the feet will slowly start to disappear.
  • The eyelids will be quite big and prominent and will cover almost all of your baby’s eyes.
  • This is also the week when the taste buds will start to form on your baby’s tongue.

6. At 9 Weeks:

  • By now your baby will measure about 2.3 cm and will weigh less than 2 gm.
  • Your baby’s eyelids will now completely cover the eyes and will be fused together. He won’t be able to open them until the 26th week.
  • At this stage, your baby’s tiny earlobes will also be visible for the first time.
  • By now, your unborn baby will start to look more like a human baby. The wrists will develop better, and the ankles will form too.
  • Your baby’s toes and fingers will also be quite prominent now, and the arms will start growing longer while they bend at the elbows.
  • Around this week, your baby’s genitalia will also start to form properly.
  • The placenta too will develop to such an extent that it can take care of most important tasks it has, such as produce the required hormones.
  • The placenta will also continue to make nutrients for your baby and flush all the waste product that your baby produces.

7. At 10 Weeks:

  • This is the week when your unborn baby will officially move from being termed as an ‘embryo’ to becoming a ‘fetus’.
  • Your baby will measure approximately 3.1 cm in height from the crown area to the rump. Also, your baby will weigh lesser than 4 gm.
  • Your unborn baby will be extremely active at this stage and will swallow fluid and kick those arms and legs.
  • By now, most of the baby’s vital organs: brain, lungs, intestines, liver and kidney, are fully formed and begin to function properly. The head will still continue to be larger than the rest of the body. It will be about half the length of your baby’s total body length.
  • Your baby’s forehead, at this stage, will be extremely big and will be positioned high on the head. However, this is a temporary thing, and it will later come back to its proper shape and place.
  • Around this week, your baby’s fingernails will be visible, as will the layer of peach-fuzz hair all over the body.
  • The spinal nerves will start to stretch outwards from your baby’s spinal cord, and the outline of the spine will also be very prominent.

8. At 11 Weeks:

  • By now your baby will measure about 4 cm in length.
  • Starting from the top of the body till the bottom, your baby will have all the organs and body parts developed by now.
  • During this week, the toes will also separate completely from the earlier webbed appearance.
  • Your baby will be quite active now and will constantly keep kicking the arms and legs and stretching them out.
  • Your baby has already started on the path to development, and most of it will already be taking place now.
  • For the next few months, the main thing that your baby will be busy doing is to grow stronger and bigger.

9. At 12 Weeks:

  • Your baby will now measure about 5.4 cm in length from the crown area till the rump and will weigh a little less than 14 gm.
  • This week, your baby will form stronger reflexes. For instance, your baby will move in reaction when you touch your belly and prod it with your fingers, even though you may not be able to feel it from the outside yet.
  • Your baby’s nerve cells will also multiply very fast, even as the many neurological connections will keep forming in the brain.
  • Your unborn baby will now be able to close the fingers, tightly squeeze the eye muscles and curl the toes.
  • By now, your baby will look more and more human as compared to the earlier features.
  • The eyes move closer to each other, unlike the way they were spaced earlier at the sides of the head.
  • The ears too will reach almost the final position where they will be placed permanently.
  • Your baby’s organs can now perform more complex tasks. The liver will start to make bile, and the kidneys will start to produce urine that will go into the bladder.

10. At 13 Weeks:

  • By now your baby will measure about 6.7 cm in length and will weigh almost 23 gm. From the size of a tiny poppy seed, your baby will now almost be the size of a pea pod.
  • It is also the week when your baby will develop some distinct fingerprints at the tip of the fingers, something that will remain unique for the rest of the life.
  • Your baby will now have sucking muscles in the cheeks. For instance, if you prod your belly a little, your baby will be able to feel the movement and start making a rooting movement. It is one of the first movements that your baby will learn which will later help the latching action during the breastfeeding stage.
  • In case you are having a female baby, the ovaries in the baby’s system will store about 2 million eggs. By the time your female baby will be born, the number of eggs will come down to about 1 million.

11. At 14 Weeks:

  • By now your baby will measure about 8 cm in length, starting from the crown area till the rump.
  • Your baby will weigh somewhere around 49 gm by now.
  • Your baby’s body will now grow faster than the head, which will finally make it all look in proportion.
  • The skin that was earlier as thin as paper will now be covered with fine downy hair, which is known as the lanugo. It will help to keep your baby’s skin protected and will almost fade off by the time of birth.
  • At this stage, your baby will also start to grow the eyebrows and have the first formation of hair on the head. However, the texture and color of the same may differ at the time of birth.
  • It is also the time when your baby will be able to form some of those first facial expressions, owing to the many impulses that will happen in the brain.
  • Your baby will be able to grasp, frown, grimace, and squint, and may even be able to suck the thumb.
  • Your baby’s kidneys will now produce urine which will move on to the amniotic fluid that surrounds your little one.

12. At 15 Weeks:

  • By now your baby will measure about 9.1 cm in length from the crown area till the rump, and will weigh somewhere around 70 gm.
  • It is also the week when your baby will get his first hiccups, preparing for the time when your baby will learn how to breathe.
  • The legs will now start to grow longer than the arms, and your baby will also be able to move all the limbs and joints.
  • By now, your baby’s genitals will be almost fully formed, and may show up on the ultrasound scan. Depending on the gender identification rules in your area, you can speak to your doctor about the same.

13. At 16 Weeks:

  • By now your baby will measure about 10 cm in length from the crown area till the rump and will weigh about 100 gm. Congratulations, your little one now is the size of an avocado!
  • Your baby will now start improvising with things around, and may find a new toy in the umbilical cord by pulling and clutching at it.
  • The head will now be more erect than what it ever was before, and the eyes will move towards the front of the head, where they will be placed as a permanent spot.
  • Your baby’s urinary tract and the circulatory system will also function properly by now.
  • By now, your baby will be able to inhale and exhale the amniotic fluid through the lungs.

[ Read: 16th Week Pregnancy ]

14. At 17 Weeks:

  • By now your baby will measure about 11 cm in length from the crown area till the rump and will weigh almost close to 140 gm.
  • At this stage, your baby’s skeleton will be rubbery, but will gradually start to become harder in the coming weeks.
  • Your baby’s spinal cord will now be coated with a protective substance known as the myelin.
  • Also, your baby will now start to develop sweat glands all over the body.
  • The umbilical cord will also grow thicker and stronger now and assist your baby in overall growth and development.

15. At 18 Weeks:

  • By now your baby will measure about 12 cm in length from the crown area till the rump and will weigh somewhere around 190 gm.
  • Your baby’s chest will now move in an upward and downward movement, such as happens while breathing.
  • The blood vessels will still be visible through the skin while the ears will shift to their final position, even though they may look slightly protruding from the head.
  • If you are going to have a female baby, the various female organs such as the vagina, the fallopian tubes and the uterus (the womb) will develop now.
  • If you are going to have a male baby, the genitals will be easily recognizable by this stage.

16. At 19 Weeks:

  • By now your baby will measure about 14.2 cm in length from the crown area till the rump and will weigh almost 240 gm.
  • Your baby will continue to swallow the amniotic fluid while the kidneys will continue to produce urine.
  • There will be a fine growth of hair on the scalp.
  • Your baby’s sensory development will be at its highest around this time. Your baby will be able to develop the various nerve cells that will help to lay the foundation for the senses such as taste, smell, hear, touch and see.
  • At this stage, there will be less production of nerve cells in the nerve cells that already exist will grow bigger. Also, they will start making more complex connections by now.
  • Now is the time when you will be able to feel the movements that your baby is making inside you.

17. At 20 Weeks:

  • Starting this week, your baby’s measurements will be taken from the crown area till the heel, instead of from the crown to the rump. By now your baby will measure about 26 cm in length from the crown area to the heel and will continue to gain good weight.
  • Your baby will now be covered in a whitish and slick substance known as the vernix caseosa. It will keep your baby’s skin protected from being inside the amniotic fluid for so long.
  • During this week, your baby will be doing more swallowing which will help to develop the digestive system. Once the amniotic fluid goes inside your baby, the body will absorb the water and flush off the rest of the liquid to the bowel area.
  • Your baby’s bowel area will keep accumulating the residue of the digestive system, which will be a sticky substance known as the meconium. It will finally come out of your baby’s system after birth, in the first motion that your baby will pass.

18. At 21 Weeks:

  • By now your baby will measure around 27 cm in length and will weigh somewhere around 360 gm.
  • By this week, your baby’s eyebrows and the eyelids will be completely developed, and your baby will also be able to blink.
  • If you are having a male baby, the testicles will come down from the pelvis towards the scrotum in the next few weeks.

19. At 22 Weeks:

  • By now your baby will measure about 28 cm in length and will weigh somewhere around 430 gm.
  • Your baby will now start to look more like a newborn, but a very thin one because the baby fat has not yet developed.
  • The skin will still look very wrinkled and transparent because your baby is due to gain more weight.
  • Your baby’s lips will be distinctly visible by now, and the eyes will form the way they will later be at birth. However, the iris, which is the colored part of the eye, will still not be pigmented, something that will happen later.
  • During this week, the pancreas will also develop at a steady pace. It will help your baby in producing the essential hormones.
  • At this stage, tiny tooth buds will start to develop near your baby’s gums, marking the stage for the teeth to set in later.

20. At 23 Weeks:

  • By now your baby will measure around 29 cm and will weigh somewhere around 500 gm.
  • Your baby will be able to hear much better and may also try to imitate various sounds, such as your voice, your heart beat or even the rumbling sound in your stomach.

21. At 24 Weeks:

  • By now your baby will measure around 30 cm and may weigh somewhere around 600 gm.
  • Your baby’s brain will continue to grow fast, and the taste buds will be fully developed by now.
  • Your baby’s footprints as well as fingerprints will still continue to form.
  • The lungs will now develop various branches in the respiratory system.
  • Your baby will also develop cells that will help to produce a substance known as surfactant. It will help to inflate your baby’s air sacs at the time of birth.

22. At 25 Weeks:

  • By now your baby will measure around 35 cm and may weigh somewhere around 660 gm.
  • Your baby will now start developing some baby fat, and the skin will become smoother instead of looking wrinkled.
  • At this stage, your baby’s sensory perceptions will be quite strong. For instance, if you shine a bright light towards your belly, your baby will turn away its head.

23. At 26 Weeks:

  • By now your baby will measure around 36 cm and may weigh somewhere around 760 gm.
  • Around this time, your baby will start opening the eyes and may even be able to hear you talking to others.

24. At 27 Weeks:

  • By now your baby will measure around 36 cm and may weigh somewhere around 875 gm.
  • Your baby will be able to open and close the eyes, will sleep and wake up at regular intervals and may also be sucking a thumb.
  • The tissues in the brain will be developing at this stage, and according to some, your baby will now start to dream.

25. At 28 Weeks:

  • By now your baby will measure around 38 cm and may weigh somewhere around 1 kg.
  • Your baby will also be able to open and shut eyes and turn the head in response to bright light from outside.
  • By now the eyelashes have developed and your baby will be able to blink.
  • The bones will be almost developed but will remain soft.

26. At 29 Weeks:

  • By now your baby will measure around 39 cm and may weigh somewhere around 1 kg.
  • By now the hair will be ready on the head.
  • If you are having a male baby, the testicles will move from near the kidneys to the scrotum through the groin area.
  • If you are having a female baby, the clitoris will be quite prominent.
  • Your baby’s head will also grow bigger now to make way for the growing brain.

27. At 30 Weeks:

  • By now your baby will measure around 39 cm and may weigh somewhere around 1.3 kg.
  • The lungs and digestive tract will be almost developed by now.
  • Your baby will also be able to have some distinction between dark and light.

28. At 31 Weeks:

  • By now your baby will measure around 41 cm and may weigh somewhere around 1.5 kg.
  • Your baby’s body will develop more baby fat and fill up the arms and legs.
  • The movements will now start to slow down a little, especially as there will be less room to move around.
  • The organs will keep developing, and your baby will also continue to flush water from the bladder.

29. At 32 Weeks:

  • By now your baby will measure around 42 cm and may weigh somewhere around 1.7 kg.
  • Your baby will continue to inhale the amniotic fluid, and the skin will also turn very smooth now.
  • If you are having a male baby, the testicles will move down from the abdomen into the scrotum.

30. At 33 Weeks:

  • By now your baby will measure around 44 cm and may weigh somewhere around 2 kg.
  • At this stage, your baby will probably turn in a head down position, to start preparing for the birth.
  • The skull will still be very soft, but the other bones in the body will start to become harder.
  • In the case of a first pregnancy, the baby’s head may move into the pelvis and press against the cervix. In the case of a subsequent pregnancy, it may happen a week before you get into labor.

31. At 34 Weeks:

  • By now your baby will measure around 45 cm and may weigh somewhere around 2.2 kg.
  • Your baby will now grow rounder as the baby fat develops.
  • Your baby’s hearing senses are also fully developed by now, which means they will be able to hear your voice when you talk.

32. At 35 Weeks:

  • By now your baby will measure around 46 cm and may weigh somewhere around 2.4 kg.
  • Your baby will now have a full set of finger and toenails and also kidneys that are fully developed.
  • Your baby’s liver will also start to flush some of the waste products.

33. At 36 Weeks:

  • By now your baby will measure around 47 cm and may weigh somewhere around 2.7 kg.

34. At 37 Weeks:

  • By now your baby will measure around 48.6 cm and may weigh somewhere around 2.8kg.
  • The downy layer of hair known as lanugo will now almost shed off completely, as well as the white protective coating known as the vernix caseosa. Your baby will swallow all of it and store it in the bowel, which will come out after birth in the first bowel movement. All of this will come out as your baby’s first stool, which will be black in color and is called the meconium.

35. At 38 Weeks:

  • Your baby could be born any time now.

It is surely a magical experience to learn how your baby develops inside you all through pregnancy. Remember that not all babies will develop in the same way, and some may develop a little slower while some may develop a little faster than others. Your doctor will monitor your baby’s growth constantly, so make sure you ask about any queries or concern you may feel.

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