Week by Week Fetal Development
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In week one of pregnancy, you won't even be pregnant yet! While most women conceive during the second week of their cycle-when they ovulate-the baby's gestational age is based on the end of your last period. Learn more in this fetal development vide
Transcript: In the beginning, you won't even know you're expecting yet. Meanwhile, your baby will be busy moving...
In the beginning, you won't even know you're expecting yet. Meanwhile, your baby will be busy moving in! The beginning of pregnancy may be confusing-after all, the first week is medically just your menstrual period. Calculation of gestational age depends on a number of factors and generally assumes a 28-day menstrual cycle length. Because your baby's expected delivery date is determined from the FIRST day of your LAST period, this week counts as part of your 40-week pregnancy even though your baby hasn't even been conceived yet! That will happen during the end of week two--again, assuming a 28-day cycle length-when one of your ovaries will release a ripe egg, which will pass into a fallopian tube. There, your egg will wait for 12 to 24 hours for the arrival of one of your partner's tens of millions of sperm. After the sperm arrives in your fallopian tube, it will combine with your egg, and merge into a fertilized egg, or zygote. It's interesting to note that it is the sperm that carries the chromosome that determines sex! At this point, the zygote's sex has been determined by either a male Y-chromosome, or female X-chromosome. At this point, your little zygote will begin the journey from fallopian tube to uterus. As it travels, the zygote will divide until it becomes a mass of 16 identical cells, which-upon reaching the uterus-is called a morula. The morula fills up with what will become amniotic fluid and changes monikers yet again. You're now carrying a blastocyst. Near the end of your third week after the first day of your last menstrual period, the blastocyst will attach itself to the endometrium, or the lining of the uterus. This process is called implantation and creates an essential connection between you and your baby. The endometrium will eventually develop into what will sustain your baby throughout the pregnancy-the placenta. But in the meantime, this lining will provide nutrients and remove wastes for the blastocyst. The newly implanted pregnancy produces hCG, human chorionic gonadotropin, which tells your ovaries to stop releasing eggs, and triggers the production of estrogen and progesterone. hCG is the chemical which shows up in your urine to turn a pregnancy test positive, so if you test at this point you may already see a positive result. Congratulations, mom-to-be. The end of this third week marks the OFFICIAL beginning of your pregnancy journey.More »
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During weeks 9 to 12 of pregnancy your little one will grow rapidly. Find out how your baby will grow in this video.
Transcript: If you've felt like you're asleep on your feet during the past three months, it's little wonder. Your...
If you've felt like you're asleep on your feet during the past three months, it's little wonder. Your rapidly growing baby has just made the progression from embryo to fetus! That means that your little guy or gal is just that...His or her genitals are beginning to show definitive signs of male or female gender. And your baby is bigger, as well. It's grown to about two and a half inches, or the length of a plum. Although that may sound small, it represents a doubling in size during this month alone! During this period, your baby will begin to move his or her arms and legs, but you won't feel these butterfly movements yet. You'll have to wait another two months or so for that! Bones and cartilage are forming inside your baby, and knees, ankles, and elbows are present now. In addition, teeth are developing under your child's gums, although they won't make an appearance until after birth. Guess what else? Your baby is producing urine, digestive juices, white blood cells, hormones and, if it's a boy, testosterone! During the last week of month three, your baby's body systems are almost completely formed. At this point, he or she will enter the maintenance phase, during which all of these systems will continue to mature and grow. While your baby is having a grand time growing, you're probably feeling the sleepy effects. That "drag-your-feet" feeling is a normal and frequent symptom of early pregnancy. The reason is simple: Growing a baby is hard work! While your metabolism and hormone levels have increased, your blood sugar and blood pressure have dropped...leaving you feeling like you ran a marathon. In addition, some of pregnancy's more awkward side effects are probably starting to show: Burping and passing gas. The pregnancy hormone progesterone relaxes the muscles in your digestive tract, allowing more time for nutrients to be absorbed. This slowed digestion is great for your baby, but may leave YOU feeling bloated and gassy. You may also experience bouts of dizziness, also due to progesterone. The hormone increases the blood flow to your baby, but slows the return of blood to you. This can lead to that light-headed feeling. You can often lessen dizziness by sitting with your head lowered between your knees while taking deep breaths. Once the feeling passes, have something to eat or drink. While dizziness and gassiness are no fun, you'll be happy to hear that the nausea, constant urination, and breast-tenderness that were with you in the beginning will usually start to abate by the end of month three. And you may have started to notice a slight rounding of your lower abdomen. After all, your uterus has now reached the size of a grapefruit and is rising up from the pelvis into this area! Congratulations! You've almost completed your first trimester. Your baby is now a fetus and you have 28 more weeks to grow and change together!More »
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This is the week most women find out they are pregnant. It is also the time when the embryo is just about the size of a poppy seed. Learn more about fetal development week 4.
Transcript: You probably just found out that you're pregnant and now you want to know what your little guy-or girl-is...
You probably just found out that you're pregnant and now you want to know what your little guy-or girl-is up to! Even though you didn't know you were pregnant, your baby has been growing since the moment of conception! By now, your baby is an embryo the size of a poppy seed -that's 10,000 times as big as she was at conception! The embryo now has distinct layers that will eventually develop into your baby's organs and body parts. All around your baby, a support system is coming into place. Your placenta is actively developing now. In fact, placental cells are actually tunneling into the lining of your uterus, creating a way for your blood flow to supply the placenta with the nutrients and oxygen that the placenta will then provide to your growing baby. Three other key parts of your baby's support system are also now present: the amniotic sac, which will surround and house your baby for the next nine months the amniotic fluid, which is inside the amniotic sac and protects and supports your baby. And the yolk sac that is delivering nutrients to your baby while your placenta - which will eventually produce your baby's red blood cells - forms. Check back in next week for your baby development video update!More »
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The changes during week 9 of pregnancy will determine what your baby's face will look like. Watch this video about the transformation your baby will go through.
Transcript: In the early stages, your baby's head develops much faster than the rest of its body, so he or she will...
In the early stages, your baby's head develops much faster than the rest of its body, so he or she will be quite top heavy in this, the ninth week of your pregnancy. At this point your embryo's facial features are becoming more distinctive by the day! The eyes are fully formed now, though they're still fused shut. And earlobes, nose, nostrils, and mouth have all begun to form. By the end of this week, your embryo will measure 2/3 of an inch and weigh just a fraction of an ounce...in other words, that baby in your belly is about the size of a grape. Also changing this week is your baby's heart, which will finish splitting into four chambers and begin to form valves.More »
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Your fetus is busy doing a number of things during week 10 of pregnancy. Find out what your baby is up to in this video.
Transcript: Tiny baby teeth buds also start developing, as do internal reproductive organs, like testes or ovaries....
Tiny baby teeth buds also start developing, as do internal reproductive organs, like testes or ovaries. Your embryo's other systems and organs are all essentially present and accounted for by now, though they will, of course, continue developing. And the news in terms of your placenta, is that it is now mature enough to fully support the developing pregnancy, which means it can produce hormones, as well as feed your baby. What a busy few days for you and your little one! For more video updates, check back next week.More »
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You fetus will try to suck its thumb for the very first time during week 13 of pregnancy. Check out this video to find out more.
Transcript: Your little one is now probably able to put that teeny thumb in his or her mouth this week! Although...
Your little one is now probably able to put that teeny thumb in his or her mouth this week! Although those sucking muscles won't be quite up to the task of doing much with that thumb, your little one will likely take comfort in just having that thumb in his or her mouth. This week, your baby is about three inches long, the size of a clementine. And with this growth, your fetus's large head is finally becoming more proportionate to the size of the rest of the body, Although you still won't know the sex of your child, if you're having a girl, her ovaries will now be home to more than two million eggs! In other news, your baby's most distinctive characteristic-fingerprints-have fully formed on the fingers and toes. Want know what's up with your 14-week-old fetus? Check back in a few days for your next video update!More »
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Did you know that during fetal development week 14, your baby is roughly the size of a peach? Find out what other changes your baby will go through.
Transcript: Your fetus shed that fish-like tail a few weeks ago, but now begins to sprout a coating of downy fur!...
Your fetus shed that fish-like tail a few weeks ago, but now begins to sprout a coating of downy fur! This ultra fine layer of hair, which is called lanugo, will continue to grow throughout the rest of your pregnancy, until it is shed shortly before birth. Meanwhile, your baby's body is growing significantly faster than the head at this point, which sits atop a more prominent neck. This week, that ever growing fetus is about the size of a peach, or 3 1/2 inches long and now weighs about 1 ounces. By now, your baby's arms are proportionate to the body, although the legs still have some growing to do. And while you still can't see them just yet, your baby's genitals have fully formed by this week. In addition, the liver has started to produce bile and the thyroid gland will begin to make thyroid hormones that will regulate metabolism. Wonder what else your little one has in store? Check back next week to get your next video update!More »
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Week 15 of pregnancy is a very exciting time, as you can find out whether you are going to have a baby boy or girl. Learn more through the video.
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By the time you get to fetal development week eighteen, your baby can probably hear you talk, or sing! Learn more about the baby’s development in the video.
Transcript: You better start brushing up on your storytelling and song singing abilities this week, because your...
You better start brushing up on your storytelling and song singing abilities this week, because your baby may be listening! Now that your baby's ears have moved to their final position on the head, the bones of the middle ear and auditory nerve endings from the brain are developing. This means that your fetus will probably be able to hear sounds like your heartbeat and blood rushing through the umbilical cord. At this point, your little one may even be startled by a sudden loud noise! And if you haven't yet done so, you'll probably start to feel those butterfly kicks of surprise, as well as some more strident jabs this week. From crown to rump, your ever-growing baby will measure about 5 inches long, and weigh seven ounces about the size of a bell pepper! In addition to ongoing brain development, a protective, insulating coat of myelin has begun to grow around your baby's nerves, a process that will continue through your baby's first year. This is why many pregnant women are advised to supplement with Omega-3 essential fatty acids so talk to your practitioner about what is right for you. For more on your little one's development, check back during your nineteenth week!More »
Last Modified: 2013-05-03 | Tags »
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Week 21 of your pregnancy will see a number of exciting changes in your baby. Check out this video and find out about the changes your baby will go through.
Transcript: Your fetus still relies on you for most things, but this week, your baby will start to learn a whole...
Your fetus still relies on you for most things, but this week, your baby will start to learn a whole new lesson in self-reliance. Although your baby still gets most of his or her nourishment directly from you via the placenta, your little one's intestines have further developed, and your baby will begin absorbing small amounts of sugar from the amniotic fluid. During week 21, your ever-growing fetus weighs about of a pound and is comparable to a carrot's ten and a half inches in length. If you're having a little girl, her vaginal canal will start to form this week. And no matter your fetus's sex, his or her bone marrow spaces are now developed enough to start making red blood cells. Previously, this was done by your baby's liver and spleen, but both of these organs will retire red blood cell production in the coming weeks. Phew! If you think this week was interesting, check back to see the surprises that wait in week 22!More »
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During week 22 of fetal development, your baby will start sucking on its thumb. Check out this video for more information about this developmental stage.
Transcript: This week your fetus will begin to discover its sense of touch. Because your baby's brain and nerve...
This week your fetus will begin to discover its sense of touch. Because your baby's brain and nerve endings are almost fully formed, he or she will begin experimenting with this newfound sense! As such, an ultrasound may show your baby stroking his face, sucking her thumb, or feeling other body parts. And now that your fetus has officially hit the one pound, 11-inch mark, he'll really start to look like a person this week. Of course, he's still covered with that downy coating of lanugo, and he also sports deep wrinkles of skin on his body. But don't worry: Before your fetus is ready to be born, he'll shed that fur and will also fill in the wrinkles with oh-so-pinchable baby fat! In other developments, a baby girl's vagina is almost fully formed now, while a boy's testes will begin to descend this week. And deep within your baby's belly, the pancreas continues to grow and get ready to produce vital hormones. Want to know more? Check back right here for your weekly fetal development update!More »
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During week 23 of pregnancy, you'll become more aware of your baby's movements. Find out more about this by watching the video.
Transcript: Can you believe that just a few weeks ago you could barely discern your baby's fluttering movements?...
Can you believe that just a few weeks ago you could barely discern your baby's fluttering movements? By now, there's no doubt that you'll feel your little martial artist as he or she kicks, squirms, and somersaults in your belly. In fact, you'll be so attuned to your little one's movements that you'll know your fetus's sleep/wake schedules. This can be frustrating if they're different from your own, but just look at this as great practice for your baby's eventual arrival! The reason it's so easy to feel your fetus now is that your baby is much bigger. In fact, your little one weighs in at about one pound. And as your baby grows, he continues to prepare for the real world with ever keener senses. In particular, your fetus's hearing will allow him to discern loud, disruptive noises, like the dog barking or the vacuum cleaner. Exposure to these sounds in the womb will mean that your baby will unlikely be fazed by them once he arrives-which is good news for you! For more on your baby's impressive development, check back right here for your weekly video update.More »
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