Fetal Development: Your Baby's Journey from Conception to Birth

Sperm Meets Egg: Weeks 1 to 3 of Pregnancy

A woman's due date is calculated from the first day of her last menstrual period. Conception occurs two weeks from that day -- that's when you're truly considered to be pregnant! Millions of sperm swim upstream on the quest to fertilize an egg. Only one successfully penetrates the egg, forming the genetic makeup that will determine the sex, physical appearance, intelligence, and personality of the baby. Watch the ovulation process occur by clicking on the video above.

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An Embryo Forms: Weeks 4 to 8 of Pregnancy

Chances are you have no idea you're pregnant yet -- but your body is already hard at work. By the 4th week of your pregnancy, the ball of cells that is developing into your baby is the size of a poppy seed. By the 5th week, the ball of cells resembles a tadpole and is the size of a peppercorn; the development of the brain, spinal cord, and heart are under way, and facial features begin to form. An umbilical cord connects the baby to your body. Watch as the egg undergoes its wondrous transformation to embryo.

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Embryo to Fetus: Weeks 9 to 12 of Pregnancy

At week 9, your baby has graduated from embryo to fetus. It is still too early to determine whether the baby is a boy or girl, but you'll soon feel the jerks felt from baby's hiccups -- one of the earliest moves a fetus makes. Facial features continue to develop and by the end of 10 weeks, Baby has developed 90 percent of the anatomical structure adults have.

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Second Trimester Begins: Weeks 13 to 17 of Pregnancy

Congrats! You are now entering your second trimester. All of your baby's internal organs have formed and will continue to mature through the second and third trimesters. Though his eyes remain closed, your baby can now begin to hear. Talk and read to him so he can get to know the sound of your voice! Watch to see the new movements and expressions he can make.

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Feeling Baby Move: Weeks 18 to 21 of Pregnancy

You'll start to feel your baby's fluttering movements (called quickening) between now and 22 weeks. Get ready, mama: Feeling the baby kick is one of the most magical parts of being pregnant. By the 22nd week, your baby is as big as a coconut. During this period, you can also find out whether you're having a boy or a girl!

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Boy or Girl: How Genetics Determine Your Baby's Gender

The process by which your baby becomes a boy or a girl, according to what's written in the baby's genetic code, is awe-inspiring. Women have two X chromosomes, and men have an X and Y chromosome; each sperm carries one of the two, leading the male's sperm to determine the baby's sex. Humans have about 25,000 genes, but only one gene located on the Y chromosome is required for male development. During week 7, the anatomical differences between male and female determined by the gene begin to take place. See how the transformation unfolds.

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Developing Senses: Weeks 22 to 25 of Pregnancy

Your baby now weighs a full pound and her ability to see, hear, smell, taste, and feel is getting stronger each day. Vocal cords have developed and she's beginning to recognize your voice and listen to the sounds of the things going on in your body. Can she breathe, too? Watch to see how her senses are already working.

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Sleep Cycles: Weeks 26 to 30 of Pregnancy

You're in your third trimester! By week 28, your baby has begun to open his eyes, blink, and practice breathing. At this point, he is awake and asleep at very specific times of the day. After 30 to 90 minutes of sleeping, he might give a kick to indicate he's awake. It's also possible he's begun to dream. Watch to find out more about your baby's sleep patterns and what they mean.

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Growing Big: Weeks 31 to 34 of Pregnancy

Your baby now weighs about three pounds, roughly the size of a melon. She'll continue to gain about a pound and a half per week until she's born. Your body is sending her antibodies that will protect her from infection. See what other new developments your baby's body is making as she prepares to exit the womb.

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Your Baby Is Almost Here: Week 35 of Pregnancy to Birth

At long last, you're about to meet your son or daughter! In preparation for birth, your baby is now upside down in your uterus. If he's not, your doctor may be able to perform some techniques to prepare him for delivery. Once your baby's in the upside down position, his head will rest against your cervix, which is opening or dilating so he can pass through the birth canal. Watch the miraculous journey your baby will go through as he (or she) exits your uterus and enters the world.

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