Source: http://www.fitpregnancy.comWeek 25
Your baby weighs 1 1/4 pounds and is a little more than 11 inches long, about the size of a small bag of sugar. In the last third of pregnancy, she'll double and triple her weight. Your dexterous baby can touch and hold her feet and make a fist. Your partner may be able to hear her heartbeat by pressing his ear against your belly. Your baby has a regular sleep schedule now and active and inactive periods. You may or may not be able to discern what those periods are. Her nostrils, which have been plugged, open up.
Week 26
Your baby weighs about 1 1/2 pounds and has undergone a growth spurt in the past few weeks. From weeks twenty to twenty-eight, she almost doubles in height and now would be about a foot tall if she could stand. This week marks a major milestone in your baby's hearing and sight. Your baby's hearing system (cochlea and peripheral sensory end organs), which began fine development during week eighteen, is now completely formed, and over the next few weeks, she'll become increasingly sensitive to sound. In about a month, you'll feel her jump if she hears a sudden loud noise. Sound passes easily into your uterus, which helps her ears develop. Her eyes are almost fully formed. Did you know that all babies have blue eyes in the womb, no matter what their genetic inheritance is? A baby's eyes don't get their final color until a few months after they are born. The air sacs of the lungs, called alveoli, will be developed by the end of this week and will begin to secrete a substance called surfactant that keeps the lung tissue from sticking together.
Week 27
Your baby weighs about two pounds and is about 12 to 15 inches long, about the size of a small pot roast. If your baby were born now, he would have an excellent chance (85 percent) of surviving. He still isn't fully formed and would probably not be able to breath by himself. He would need to stay in an incubator to keep his body temperature regulated, and he would have a weak liver and immune system. (Fact: Babies have more taste buds at birth than they will have later in life. Newborns can sniff out and tell the difference between their mother's milk and someone else's.)
Week 28
Your baby has doubled her weight in the past month and is the size of a bag of flour. She now weighs almost 2 1/2 pounds. Her total length is nearly fifteen inches. Your baby's lungs are now capable of breathing air! This is big news. It means if the baby is born from now on, she'll be able to survive with less medical intervention. Your baby's main job right now is to put the finishing touches on major organ systems, such as her brain, lungs, and liver. As you can probably tell, she's also working on gaining layers of fat. Her body fat is about 2 to 3 percent. Your baby's eyes, which were covered by her eyelid folds at the sixth week of development, are capable of opening this week. Her sucking and swallowing skills are improving.
Week 29
Your baby is about two and a half pounds and would be between fifteen and seventeen inches tall if she could stand. Your baby's adrenal glands are producing a chemical which will be made into estriol (a form of estrogen) by the placenta. This estriol is thought to stimulate the production of prolactin by your body, and the prolactin makes you produce milk. So even if your baby comes early, you'll still be able to breastfeed. Each passing week improves the likelihood that your baby will be born strong and healthy. Her brain can detect rhythmic breathing and control body temperature, so she's less likely to need breathing assistance should she be born early. She's growing eyelashes, adding fat, and developing her brain. Because of brain wave activity, researchers have speculated that babies can even dream at this time!
Week 30
You baby's length is about 16 inches—about as long as a laptop computer—and she measures almost 11 inches from crown to rump. She weighs approximately 2 1/2 to 3 pounds. From now until delivery, every baby will gain weight at a more individual rate. Your baby has doubled in height over the past six weeks, and from now until delivery, she'll gain only a few more inches in length. Don't worry if she's in a strange position (what your care provider might call a "transverse lie"). There's still plenty of time for her to get settled into the head-down (cephalic) position for birth. She's floating in about 1 1/2 pints of amniotic fluid and has some room to move. Your baby's most important organ, her brain, continues to develop at a rapid pace. Her eyes are able to track light, and some researchers have theorized that exposing your belly to light may stimulate development. Try moving the beam of a flashlight slowly over your belly in a dim room, and see if she reacts.
Week 31
You baby weighs between 2 1/2 and 3 1/2 pounds. She continues to gain weight at a faster pace than she lengthens, which will give her those cute chubby cheeks. She's about fourteen to sixteen inches tall, although individual growth rates vary. Your baby begins to run out of room as she puts on weight. You should feel about ten kicks an hour. Some care providers suggest keeping a "kick chart" by writing down how many kicks you feel in an hour, so that you are aware if there's a decrease in activity. Other care providers may advise that as long as it feels like the baby's active, there's no need to keep notes. If you do sense a decrease in activity, try drinking a large glass of juice. If that doesn't make the baby energized, or makes her less energized than she usually would be, call your care provider.
Week 32
Your baby weighs about 4 pounds and is about fifteen to seventeen inches tall. Photographs of babies in utero at this stage show their skin becoming less translucent and pinker, as layers of fat are deposited under the skin. Her skeleton is rapidly ossifying (turning from cartilage into solid bone), which means that kicks will become visible through your shirt as the trimester progresses. Well-placed kicks under your ribs can take your breath away!
Week 33
Your baby's crown-to-rump length is about 11 1/2 inches. She weighs about 4 1/2 pounds and gains about eight ounces every week. Your baby has probably moved to the head-down position and may descend into your pelvis at any time in the next six weeks and begin to press into your cervix. This position not only prepares her for birth but allows blood to flow to her developing brain. The dark quiet of your womb is perfect for this activity. Right now, your baby is also in the process of receiving your antibodies. If she were born right now, her immune system would be immature, and extra care would need to be taken to keep her in a sterile environment.
Week 34
Your baby weighs five pounds or more, about the size of a bag of sugar. She will continue to gain about two or more pounds in the next six weeks. Now that your baby's brain has formed billions of neurons, it must accomplish the even more complex feat of hooking the neurons and synapses together. Your baby's brain is forming trillions of connections, making it possible for her to learn in the womb. All of this brain development may be the reason that your baby sleeps frequently at this stage. She may even be dreaming—her eyes dart around rapidly just as an adult's might in REM sleep. Your child's development is in no way complete at birth. In the first year after birth, a baby's brain triples in size and becomes three-quarters of its adult size.
Week 35
At more than five pounds and between sixteen and twenty inches, your baby is becoming more ready for birth with every passing hour. She's the size of a small roasting chicken. Her nervous system and immune system are still maturing, and she's adding the fat that she'll need to regulate her body temperature. But, everything else, from her toenails to the hair on her head, is fully formed. If she were born now, she'd have more than a ninety-nine percent chance of surviving.
Week 36
With one month to go, your baby weighs about six pounds and is fattening. Her full length from crown to feet is about 20 1/2 inches. Has your baby's movement slowed down? If so, you shouldn't worry. Five to ten percent of all mothers report that babies start to slow down as they grow larger and get more cramped for space. Still, you should be able to feel your baby move more than ten times a day. If you're concerned, try drinking a sweet beverage, such as orange juice, and then lying on your side for a while. Most babies will wake up and start to move. If you're still concerned, contact your healthcare provider.
Week 37
Your baby has likely hit the six-pound mark by now, and her length is approximately twenty-one inches. The weight on your abdomen probably feels like twice that. Your baby is practicing her breathing, but she has increasingly less space to practice stretching and kicking. Your baby' intestines are also building up meconium, a greenish-black substance made of baby by-products such as dead cells, shed lanugo, and amniotic fluid. It'll become your little darling's first bowel movement, hopefully after she is out of the womb. Her body fat has increased to about eight percent. By birth, it'll be about fifteen percent. If your baby is a boy, his testes will have descended into his scrotum. While your baby could be born at any time, the longer she stays in, the more time she has to develop the connections in her brain in the pleasant peace and quiet of your womb. At this point, she can do all the things a newborn can, with the exception of breathing air and pooping in a diaper. Just as you're feeling stretched, your baby is being squeezed on all sides. Some of your antibodies are crossing the placenta, giving your baby's immune system some support for her first days in the world. If you breastfeed, you'll later be giving her immunities in your milk.
Week 38
The average newborn has a length of 21 1/2 inches and weighs 7 1/2 pounds. She is fully developed, though still adding connections between neurons in the brain (this continues well after birth). Her nails have been growing and now reach to the ends of her fingers and toes. Her movements are quite restricted by her close quarters.
Week 39
You're in the home stretch! After nine months of growth and development, your baby is ready to be born, or nearly so. At week 39, your baby is fully developed and anywhere from 17-23 inches long and weighs 6-10 pounds. Don't be frightened if your OB-GYN says your baby is large: It's extremely difficult to judge a baby's weight accurately from the outside. Your baby is adding neural connections and growing hair and still gaining weight. Researchers have theorized that when babies are ready to be born, they send a chemical signal of androgens to the placenta, which increases the production of estrogen and leads to labor. If so, it's proof of the old saying that "only a baby knows when it's ready to be born."
Week 40
Congratulations - your baby is now fully formed and ready to be born. If your due date passes, your doctor will check to see if the baby has enough amniotic fluid. If he's fine, you and your doctor may still want to discuss induction.
