Baby Is the Size of a What?? Tracking Fetal Development In Pregnancy Weeks 4 - 40 Fetal Development First Trimester Second Trimester Third Trimester
From the day of conception, your baby goes through a remarkable fetal development process. Comparing a growing baby's size to a fruit or vegetable has become a tradition with parents-to-be. So, here's the scoop on how big your baby is week to week! Be sure to check out our Pregnancy Weekly.
Week 4: Your embryo is about the size of a poppy seed. Your poppy seed is actually two layers right now called the epiblast and the hypoblast. The layers will become hair, skin, eyes, nervous system, heart, reproductive organs, bones, muscles. All our vital parts.
Week 5: 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.
Week 6: Baby is the size of a lentil. His oversized head now has places forming for eyes, nose and mouth. Tiny arms and legs are beginning to emerge as buds on both sides. And guess what starts to make its appearance? The umbilical cord.
Week 7: Your baby is about the size of a blueberry and resembles 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.
Week 8: Baby is about the size of a kidney bean this week. And guess what? She looks more like a baby and not an alien. The nose is beginning to get defined and his eyelids are forming.
Week 9: Baby is slowly starting to look like a baby, and he's 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.
Week 10: All of your baby’s vital organs are accounted for and now start to grow rapidly. Baby is swallowing fluid, and his kidneys, brain, liver and intestines are beginning to function. At the size of a kumquat, he can bend his little arms and legs – and is kicking away.
Week 11: About the size of a fig, your 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.
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.
Week 13: Baby is about 3 inches long now, weighs almost an ounce and is the size of an egg. Baby needs to stay out of trouble, because tiny fingerprints are now forming.
Week 14: Has your baby morphed into an old man this week? He can frown, pee, grimace and even squint now! Baby is the size of a large lemon (cue sour expression) and weights 1 1/2 ounces.
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, so there’s even more movement going on now.
Week 16: Baby is about the size of an avocado now. 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.
Week 17: Your baby’s skeleton is now changing from cartilage to bone (soft to hard). Body fat is starting to form and this will continue until Baby is born. Your baby weighs about 5 ounces now and is the size of a pear.
Week 18: At about 7 ounces, your little pumpkin is 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.
Week 19: Your baby is getting a little cheesy this week. Really. A greasy, white cheese-like substance called vernix caseosa is now covering your baby’s skin. Baby weighs about 8 1/2 ounces and the size of a large tomato.
Week 20: Your 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, the black, sticky substance forming the first feces of a newborn.
Week 21: Baby now weighs between 11 and 12 ounces and is about as long as really big carrot. Amniotic fluid is Baby’s drink of choice right now – it keeps him hydrated, helps him practice swallowing and encourages growth of the intestinal tract.
Week 22: One pound. That’s about what your baby weighs right now. Baby is the same weight as a 1-pound box of sugar. The eyelids are still fused together, but Baby can now sense dark from light.
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.
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.
Week 25: Cauliflower is all the rage – and your baby is now about as big as one! At 13 1/2 inches long and weighing 1 1/2 pounds, Baby is beginning to get some fat on her tiny body.
Week 26: Right now your baby weighs about 1 2/3 pounds and is 14 inches long, about the size of a bunch of kale. If you are having a boy, his testicles are now descending into his scrotum, which will take two to three months.
Week 27: Baby is now 14 1/2 inches long, weighs about 2 pounds and is as big as a bunch of broccoli. Baby's lungs are not fully developed yet, but there is a chance he could breathe on his own with medical help if born now.
Week 28: At 2 1/4 pounds and almost 15 inches long, Baby continues to add body fat to plump up her body and is about the size of a head of lettuce. Baby is blinking her eyes that are beginning to get color now, and she has eyelashes.
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 his head is getting bigger to meet the needs of his ever-growing brain.
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.
Week 31: At around 3 1/3 pounds and 16 inches long, your baby has gone from a cabbage to a coconut! Trillions of brain connections between nerves are being formed so he can process information from all five senses.
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.
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 remained not fused together.
Week 34: Close to 4 3/4 pounds and up to 18 inches long, your baby is now as big as a large cantaloupe. Baby’s tiny fingernails have grown to the tips of her fingers, getting ready for that first tiny manicure!
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.
Week 36: Baby weighs about 6 pounds now and may be 18 to 19 inches long, about as long as a head of romaine lettuce. Baby’s growth is about to slow way down.
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.
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 that trip into the world.
Week 39: At around 7 to 8 pounds and 20 to 21 inches long, Baby is about the size of one of those adorable mini watermelons. Baby’s skin is now pink and smooth.
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!
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