How your baby's growing: Your baby now weighs about 2 1/2 pounds (like a butternut squash) and is a tad over 15 inches long from head to heel. His muscles and lungs are continuing to mature, and his head is growing bigger to make room for his developing brain. To meet his increasing nutritional demands, you'll need plenty of protein, vitamins C, folic acid, and iron. And because his bones are soaking up lots of calcium, be sure to drink your milk (or find another good source of calcium, such as cheese, yogurt, or enriched orange juice). This trimester, about 250 milligrams of calcium are deposited in your baby's hardening skeleton each day.

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How your baby's growing: By this week, your baby weighs two and a quarter pounds (like a Chinese cabbage) and measures 14.8 inches from the top of his head to his heels. He can blink his eyes, which now sport lashes. With his eyesight developing, he may be able to see the light that filters in through your womb. He's also developing billions of neurons in his brain and adding more body fat in preparation for life in the outside world.

See what your baby looks like this week.

How your baby's growing: This week, your baby weighs almost 2 pounds (like a head of cauliflower) and is about 14 1/2 inches long with his legs extended. He's sleeping and waking at regular intervals, opening and closing his eyes, and perhaps even sucking his fingers. With more brain tissue developing, your baby's brain is very active now. While his lungs are still immature, they would be capable of functioning — with a lot of medical help — if he were to be born now. Chalk up any tiny rhythmic movements you may be feeling to a case of baby hiccups, which may be common from now on. Each episode usually lasts only a few moments, and they don't bother him, so just relax and enjoy the tickle.

See what your baby looks like this week.

How your baby's growing: The network of nerves in your baby's ears is better developed and more sensitive than before. He may now be able to hear both your voice and your partner's as you chat with each other. He's inhaling and exhaling small amounts of amniotic fluid, which is essential for the development of his lungs. These so-called breathing movements are also good practice for when he's born and takes that first gulp of air. And he's continuing to put on baby fat. He now weighs about a pound and two-thirds and measures 14 inches (an English hothouse cucumber) from head to heel. If you're having a boy, his testicles are beginning to descend into his scrotum — a trip that will take about two to three days.

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How your baby's growing: Head to heels, your baby now measures about 13 1/2 inches. His weight — a pound and a half — isn't much more than an average rutabaga, but he's beginning to exchange his long, lean look for some baby fat. As he does, his wrinkled skin will begin to smooth out and he'll start to look more and more like a newborn. He's also growing more hair — and if you could see it, you'd now be able to discern its color and texture.

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How your baby's growing:Your baby's growing steadily, having gained about 4 ounces since last week. That puts him at just over a pound. Since he's almost a foot long (picture an ear of corn), he cuts a pretty lean figure at this point, but his body is filling out proportionally and he'll soon start to plump up. His brain is also growing quickly now, and his taste buds are continuing to develop. His lungs are developing "branches" of the respiratory "tree" as well as cells that produce surfactant, a substance that will help his air sacs inflate once he hits the outside world. His skin is still thin and translucent, but that will start to change soon.

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How your baby's growing: Turn on the radio and sway to the music. With his sense of movement well developed by now, your baby can feel you dance. And now that he's more than 11 inches long and weighs just over a pound (about as much as a large mango), you may be able to see him squirm underneath your clothes. Blood vessels in his lungs are developing to prepare for breathing, and the sounds that your baby's increasingly keen ears pick up are preparing his for entry into the outside world. Loud noises that become familiar now — such as your dog barking or the roar of the vacuum cleaner — probably won't faze him when he hears them outside the womb.

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How your baby's growing:At 11 inches (the length of a spaghetti squash) and almost 1 pound, your baby is starting to look like a miniature newborn. His lips, eyelids, and eyebrows are becoming more distinct, and he's even developing tiny tooth buds beneath his gums. His eyes have formed, but his irises (the colored part of the eye) still lack pigment. If you could see inside your womb, you'd be able to spot the fine hair (lanugo) that covers his body and the deep wrinkles on his skin, which he'll sport until he adds a padding of fat to fill them in. Inside his belly, his pancreas — essential for the production of some important hormones — is developing steadily.

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How your baby's growing:Your baby now weighs about three-quarters of a pound and is approximately 10 1/2 inches long — the length of a carrot. You may soon feel like he's practicing martial arts as his initial fluttering movements turn into full-fledged kicks and nudges. You may also discover a pattern to his activity as you get to know him better. In other developments, your baby's eyebrows and lids are present now.

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How your baby's growing:Your baby weighs about 10 1/2 ounces now. He's also around 6 1/2 inches long from head to bottom and about 10 inches from head to heel — the length of a banana. (For the first 20 weeks, when a baby's legs are curled up against his torso and hard to measure, measurements are taken from the top of his head to his bottom — the "crown to rump" measurement. After 20 weeks, he's measured from head to toe.)

He's swallowing more these days, which is good practice for his digestive system. He's also producing meconium, a black, sticky by-product of digestion. This gooey substance will accumulate in his bowels, and you'll see it in his first soiled diaper (some babies pass meconium in the womb or during delivery).

See what your baby looks like this week.