Before you can even feel or see the evidence of a baby inside
your body, he or she is growing and developing in amazing ways!
Check out each week to see the growth milestones that your baby is experiencing!

1st Trimester

Week 5: This is about the time that your period does not show and you suspect that you are pregnant. Cells organize to form everything that your baby will need, from the lungs, bladder, muscles, skin, and hair!

Week 7: Your little baby is the size of a pea with tiny facial features forming. The first layer of skin appears and the hands begin to form. Changes in the brain occur that will produce personality, senses, movement and breathing

Week 8: Your baby is now the size of a lima bean. The esophagus forms and the lungs begin to form this week as well.

Week 9: Your baby is now an inch long with moving brain waves. The outward signs of gender have appeared, although they will not be noticeable on an ultrasound for another 6-8 weeks because they are so small. The muscles are growing and getting stronger, with elbows, knees, and other limb joints becoming distinguishable.

Week 10: The intestines are forming and the baby’s hands can almost touch each other in front of its belly. The ears are almost fully developed and the eyes already have some color.

Week 11: The fingers and toes are visible. The teeth are growing in the tooth sockets although they will not be seen until the baby begins teething after birth.

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2nd Trimester

Week 12: The pancreas begins to produce insulin and the liver secretes bile that helps the body digest fats. The face is becoming more defined with a bridge of the nose and jawbones adding to the facial features.

Week 13: Around this week, the baby’s body begins to wriggle and even gets the hiccups!

Week 14: The baby begins grimacing and practicing expressions. He/she also begins to practice sucking motions that will enable eating to occur!

Week 15: Hair begins to sprout on the head and eyebrows. A downy fuzz called lanugo covers the body and the baby can actually "breathe" underwater!

Week 16: The baby is getting bigger so you may start to feel kicking. The baby’s body parts have grown to "normal" proportions. The eyelids now shut as well.

Week 17: The baby is firmly attached to the placenta through the umbilical cord. The skeleton is transforming its soft cartilage to bone.

Week 18: A fingerprint design appears and the baby may begin to suck its thumb. The placenta is now as big as the baby!

Week 19: The nerves are coated with a fatty substance called myelin that insulates the nerves so impulses can flow smoothly.

Week 20: Celebrate because you are halfway through your pregnancy. On average, your baby weighs a pound and has a rapidly beating heart.

Week 21: You may notice that your baby is both active and still at different times of the day. It is developing an internal clock around your schedule!

Week 22: The baby is covered in vernix caseosa which is a sticky white "goo" that protects the baby from not only becoming wrinkly like a prune but makes it easier to slide through the birth canal for delivery.

Week 23: The baby can now hear you! He/she can hear noises from both inside and outside the womb. Don’t be shy about talking to your baby and tell Dad to do the same.

Week 24: The lungs are now preparing to breathe and at this stage, if the baby is born early, most can survive because they are prepared with everything that they need.

Week 25: The umbilical cord is strong and thick. "Grown up" teeth are now forming.

Week 26: The spine is getting stronger and the baby is getting larger. On average, he/she is about a foot tall and weighs two pounds.

Week 27: The eyes will now open and changes in light can be detected. Eyelashes also appear at this stage.

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3rd Trimester

Week 28: The main job for the baby at this stage is to gain weight and build bulk!

Week 29: The brain is growing in power and speed and the baby’s living quarters are becoming cramped!

Week 30: On average, your baby weighs three pounds and is 17 inches long!

Week 31: The iris is giving more color to the baby’s eyes.

Week 32: The baby is practicing "breathing lessons" with its formed lungs.

Week 33: It is fun at this stage to watch your baby’s movements and determine the most active times of the day.

Week 34: The baby is now resting on the uterus and getting ready to be born! Most babies will be positioned with his/her head down to prepare.

Week 35: The toenails are formed and the baby weighs equivalent to a 5 pound bag of sugar!

Week 36: The baby’s main job in the last weeks of pregnancy is to get fat and this is a good thing! The fat will protect him/her and keep the baby healthy.

Week 37: If labor starts at this point, it is "All Systems Go!" The baby is ready to enter the world at any time between now and 40 weeks. He/she can’t wait to meet you!

Above information cited from www.parents.com. Please check out their website for more fetal development milestones.