For the nine months that you carry your baby, every week brings new developments. From a microscopic group of cells to a fully-functioning baby, the development of a baby brings complex changes and growth every week.
All pregnancies are different, and babies are born in varying sizes and with different abilities. Following a general timetable of weekly progress can help parents keep track of their developing baby.
Week 1-2. The fertilized egg grows into a ball of cells and burrows into the lining of the uterus. Cells are dividing and specializing.
Week 3. Pregnancy can be detected. Amniotic fluid begins to surround the ball of cells. Hormones are being released to help its growth.
Week 4. The size of a poppy seed, the embryo's organs begin to develop
Week 5. Three layers are developing, which will later make up all of the baby's organs and tissues.
Week 6. Nose, mouth and ears are taking shape. Blood is beginning to course through his body, which is the size of a lentil bean.
Week 7. Hands and feet are emerging. The mother's uterus has doubled in size.
Week 8. Webbed toes and fingers are emerging and eyelids are developing. Breathing tubes are forming a respiratory system and nerve cell connections are forming a nervous system.
Week 9. The baby's heart now has four chambers and his teeth buds are beginning to form.
Week 10. The fetus is kicking and moving his limbs.
Week 11. Just over 1½ inches long, the fetus can open and close his fists. His bones are beginning to harden.
Week 12. Reflexes are developing, so the fetus will squirm in response to prodding and can make sucking motions with his mouth.
Week 13. Fingerprints develop at about this week, and organs and veins are visible through the thin, transparent skin.
Week 14 - 15. Brain impulses allow the baby to squint, suck his thumb and make facial expressions. He's about 4 inches long now.
Week 16 - 17. The umbilical cord is growing stronger and thicker, and sweat glands are beginning to form.
Week 18-19. Hair is sprouting, the kidneys are making urine and the baby may be able to hear the mother's voice.
Week 20-21. The size of a banana, the baby is moving noticeably now.
Week 22. The baby looks like a miniature newborn, with wrinkly skin and a fine layer of hair, known as lanugo, covering his body.
Week 23. Blood vessels in his lungs are starting to develop, in preparation for breathing. He can swallow.
Week 24. The brain is continuing to develop, as are the taste buds.
Week 25-26.The baby is now about 13½ inches long and weighs 1.5 pounds. Nerve pathways are developing in the ears, making him more responsive to sounds.
Week 27-28. The baby can now blink his eyes and is adding body fat to prepare for life outside the womb. His eyesight is developing and he may be able to see light.
Week 29-30. The baby's head is growing bigger to handle his developing brain.
Week 31. A growth spurt begins. The baby can turn his head from side to side.
Week 32. The mother is gaining about a pound a week and half of that now goes to the baby. The baby has fingernails, toenails and hair. His skin is smoothing out.
Week 33. Weighing around 4 pounds, the baby is developing a hardened skeleton. His skull will remain flexible, however, for an easier journey through the birth canal.
Week 34. The baby's central nervous system continues to mature.
Week 35. The baby's size, about 18 inches long and more than 5 pounds, makes it difficult to move in the womb. Nonetheless, the mother can still feel him kick regularly.
Week 36. The baby is gaining about an ounce per day now, and is shedding his skin protectant in preparation for birth.
Week 37-38. All of the baby's organs are matured and ready for life outside the womb.
Week 39-40. The baby continues to build a layer of fat to help control his body temperature after his birth.
Week 40-42. While these weeks are cozy and safe for the baby, he is at the best time to leave the womb and join his family in the outside world.
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