Fetal Development Gallery: See How Your Baby Grows From Pregnancy Week 4 to 40! Fetal Development

The changes your baby goes through from implantation to being born into this world are truly miraculous. Here's a photo journal of your little one's journey from an embryo the size of a poppy seed to that beautiful newborn you'll hold in your arms. And be sure to learn about your pregnancy week by week by checking out our Pregnancy Weekly! 

Week 4: Your embryo is about the size of a poppy seed and is going through remarkable changes. Your poppy seed is actually two layers right now called the epiblast and the hypoblast. Until about 10 weeks, your baby’s organs will be developing. Learn more about fetal development in week 4 or pregnancy.

Week 5: Your baby is the size of a sesame seed and already has a head, front, back and a tail (relax, your baby will not be born with a tail – it gets absorbed). Baby has also morphed into three layers: the ectoderm, mesoderm and endoderm. Learn more about fetal development in week 5 of pregnancy. 

Week 6: Your baby is the size of a lentil. Tiny arms and legs are beginning to emerge as buds on both sides. Intestines, the pituitary gland, bones, the brain and muscles are also works in progress. Learn more about fetal development in week 6 of pregnancy. 

Week 7: When week 7 begins, your baby is about the size of a blueberry and resembles … well … a tadpole. When his arms and legs emerge by the end of the week, he’ll look a lot more human-like. Baby’s entire skeleton – made of flexible cartilage – will be fully formed this week, followed by actual bone soon. Learn more about fetal development in week 7 of pregnancy. 

Week 8: Baby is about the size of a kidney bean this week. The nose is beginning to get defined and his eyelids are forming. Those fingers and toes that you’ll soon count are taking shape, though right now they’re webbed. Learn more about fetal development in week 8 of pregnancy. 

Week 9: Baby is about the size of a grape. The tail your little one was sporting is gone now, and all the vital organs are in place, though still developing. The heart is dividing into four chambers and valves are making their appearance. Learn more about fetal development in week 9 of pregnancy. 

Week 10: At the size of a kumquat, Baby can bend his little arms and legs and is kicking away (sorry, you still can’t feel it). Teeny tiny finger and toenails are appearing (buh-bye webbing) and he’s resembling a peach with all the tiny hairs growing on his skin. Learn more about fetal development in week 10 of pregnancy. 

Week 11: About the size of a fig, Baby is almost fully formed already. Baby’s head makes up nearly half of his body size, so right now he’s more alien like than human (that will change soon!). At 1 1/2 inches long, Baby is kicking and moving around a lot, though it’ll be a while longer before you can feel it. Learn more about fetal development in week 11 of pregnancy. 

Week 12: Baby is the size of a lime and is about 2 1/4 inches long. All of Baby’s body systems are in place – and some are even working on their own. The thyroid is now secreting hormones, the kidneys will begin excreting urine, the pituitary gland has started producing hormones and bone marrow is making white blood cells. Learn more about fetal development in week 12 of pregnancy. 

Week 13: Baby is about 3 inches long now, weighs almost an ounce and is the size of an egg. Tiny fingerprints are now forming. Veins and other organs can be clearly seen through her skin, and tiny arm and leg bones are developing, which help your baby suck his or her thumb. Learn more about fetal development in week 13 of pregnancy.

Week 14: Baby is the size of a large lemon and weights 1 1/2 ounces. Baby is also growing lanugo, unpigmented hair that covers the body, the liver has started making bile and the spleen is producing red blood cells. Your baby also has a roof to his mouth now, an active digestive system and meconium. Learn more about fetal development in week 14 of pregnancy. 

Week 15: At 4 inches long, Baby is about the size of an apple. Baby’s thin skin is still translucent, so the tiny veins are visible. All the limbs are bendable now. Taste buds are forming, though it’ll be a while before there’s anything yummy to taste. Learn more about fetal development in week 15 of pregnancy. 

Week 16: Baby is about the size of an avocado. At about 4 ounces and 4 1/2 inches in length, Baby’s kidneys are working, the stomach is secreting bile and the heart is pumping about 25 quarts of blood daily. Learn more about fetal development in week 16 of pregnancy. 

Week 17: Baby weighs about 5 ounces now and is the size of a pear. The skeleton is now changing from cartilage to bone (soft to hard). The brain has taken over regulating Baby’s heartbeat, which beats between 140 to 150 beats per minute. Learn more about fetal development in week 17 of pregnancy.

Week 18: At about 7 ounces, Baby is about the size of a bell pepper. Myelin, a protective coating around nerve fibers in the central nervous system, is starting to form around Baby’s nerves. The brain is developing the areas that handle the senses of smell, touch, taste, sight and hearing. Learn more about fetal development in week 18 of pregnancy. 

Week 19: Baby weighs about 8 1/2 ounces and the size of a large tomato. A greasy, white cheese-like substance called vernix caseosa is now covering Baby’s skin. Learn more about fetal development in week 19 of pregnancy. 

Week 20: Baby weighs about 10 1/2 ounces and is the size of a large banana. Baby’s organs are settling into their right locations, teeth are starting to appear and he’s producing meconium. Learn more about fetal development in week 20 of pregnancy. 

Week 21: Baby now weighs between 11 and 12 ounces and is about as long as really big carrot. Baby also has eyebrows and eyelids now. Learn more about fetal development in week 21 of pregnancy. 

Week 22: Baby is the same weight as a 1-pound box of sugar. Her skin is still wrinkly and pink due to lack of fat right now, but facial features are now more distinct. Baby’s sense of touch is increasing and so is her grip. Learn more about fetal development in week 22 of pregnancy.

Week 23: Now a little over 1 pound and about 11 inches in length, Baby is about the size of an eggplant. Tiny blood vessels are forming in Baby’s lungs as is a substance called surfactant. Surfactant helps keep the lungs from collapsing and sticking together and makes breathing easier. Learn more about fetal development in week 23 of pregnancy. 

Week 24: Close to 1 1/3 pounds and as long as an ear of corn, your baby is now gaining about 5 to 6 ounces per week. The weight is not fat (yet!), but muscle, bone and organ growth. Learn more about fetal development in week 24 of pregnancy. 

Week 25: Baby is now about as big as a head of cauliflower! At 13 1/2 inches long and weighing 1 1/2 pounds, Baby is beginning to get some fat on her tiny body. She’s also pinking up a bit due to small capillaries forming and filling with blood under her still-translucent skin. Learn more about fetal development in week 25 of pregnancy. 

Week 26: baby weighs about 1 2/3 pounds and is 14 inches long, about the size of a bunch of kale. Baby’s eyes have been shut so the retina can develop, but now Baby’s eyes are open. Learn more about fetal development in week 26 of pregnancy. 

Week 27: Baby is as big as a bunch of broccoli. Baby is now 14 1/2 inches long and weighs about 2 pounds. Learn more about fetal development in week 27 of pregnancy. 

Week 28: Baby is about the size of a bunch of lettuce. At 2 1/4 pounds and almost 15 inches long, Baby continues to add body fat to plump up her body. She’s blinking her eyes that are beginning to get color now, and she has eyelashes. Learn more about fetal development in week 28 of pregnancy.

Week 29: Your baby now weighs 2 1/2 to 3 pounds and is 15 1/2 inches long, about the size of a butternut squash. The lungs continue to develop and Baby's head is getting bigger to meet the needs of his ever-growing brain. Learn more about fetal development in week 29 of pregnancy. 

Week 30: At the 3-pound mark and being about 15.7 inches long, Baby is about the size of a cabbage. Baby won’t get much longer, but will gain around 1/4 to 1/2 pound each week! Learn more about fetal development in week 30 of pregnancy. 

Week 31: At around 3 1/3 pounds and 16 inches long, your baby has gone from a cabbage to a coconut! This week, all of Baby’s senses are in full swing. Learn more about fetal development in week 31 of pregnancy. 

Week 32: At 3 1/2 to 4 pounds, 15 to 17 inches long and about the size of a head of Chinese cabbage, Baby is busy practicing those skills she’ll need once she’s born: sucking, kicking, swallowing and breathing. Learn more about fetal development in week 32 of pregnancy. 

Week 33: Baby is now over 4 pounds and may be over 17 inches long, about the size of a pineapple. His bones are hardening, though the bones in his skull will remain not fused together. Learn more about fetal development in week 33 of pregnancy.

Week 34: At around 4 3/4 pounds and up to 18 inches long, your baby is now as big as a large cantaloupe. Baby is still collecting fat, which continues to smooth out his skin. Learn more about fetal development in week 34 of pregnancy. 

Week 35: At almost 18 inches long and 5 1/4 pounds (think honeydew melon this week), besides growing in size, your baby is pretty much fully developed. The lungs may still have a little way to go, but the name of the game going forward for Baby is just gaining weight. Learn more about fetal development in week 35 of pregnancy.

Week 36: Baby weighs about 6 pounds now and may be 18 to 19 inches long. Baby is as long as the head of romaine lettuce. Bones and cartilage are not the only thing that will finish developing after birth. Her digestive system, while developed, will take a little time to get used to not having an umbilical cord to rely on. Learn more about fetal development in week 36 of pregnancy. 

Week 37: Baby weighs about 6 1/2 pounds and, at around 19 inches, is as long as a bunch of Swiss chard. These two remaining weeks of a 40-week pregnancy will allow Baby’s lungs and brain to continue to mature and get ready for life on the outside. Learn more about fetal development in week 37 of pregnancy. 

Week 38: That little ball of cells you started out with is not so little anymore! At around 7 pounds and up to 20 inches long (as long as a leek!), Baby continues to get ready for those newborn photos. She’s continuing to shed vernix and lanugo and adding more fat to those chubby cheeks. Learn more about fetal development in week 38 of pregnancy.

Week 39: At around 7 to 8 pounds and 20 to 21 inches long, he’s about the size of one of those adorable mini watermelons. While his brain is continuing to grow at a fast rate (and will for his first three years of life), his weight and length will stay about the same now. Learn more about fetal development in week 39 of pregnancy.

Week 40: A full-term baby can weigh anywhere from 6 to 9 pounds and be 19 to 22 inches long – about the size of a small pumpkin. You will meet him or her soon! Learn more about fetal development in week 40 of pregnancy.

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