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Week 1
This first week is actually your menstrual period. Because your expected birth date (EDD or EDB) is calculated from the first day of your last period, this week counts as part of your 40-week pregnancy, even though your baby hasn’t been conceived yet. -
Week 2
Fertilizations of your egg by the sperm will take place near the end of this week. -
Week 3
Now nestled in the nutrient-rich lining of your uterus is a microscopic ball of hundreds of rapidly multiplying cells that will develop into your baby. This ball, called a blastocyst, has begun to produce the pregnancy hormone hCG, which tells your ovaries to stop releasing eggs. -
Week 4
Your baby-to-be is now an embryo. Over the next six weeks, its nervous system, connective tissue, and organs will start to develop. -
Week 5
Your baby resembles a tadpole more than a human, but is growing fast. The circulatory system is beginning to form, and the tiny "heart" will start to beat this week. -
Week 6
Your baby's nose, mouth and ears are starting to take shape, and the intestines and brain are beginning to develop. -
Week 7
Your baby has doubled in size since last week, but still has a tail, which will soon disappear. Little hands and feet that look more like paddles are emerging from the developing arms and legs. -
Week 8
Your baby has started moving around, though you won't feel movement yet. Nerve cells are branching out, forming primitive neural pathways. Breathing tubes now extend from his throat to his developing lungs. -
Week 9
Your baby's basic physiology is in place (she even has tiny earlobes), but there's much more to come. Her embryonic tail has disappeared. She weighs just a fraction of an ounce but is about to start gaining weight fast. -
Week 10
Your embryo has completed the most critical portion of development. His skin is still translucent, but his tiny limbs can bend and fine details like nails are starting to form. -
Week 11
Your baby is almost fully formed. She's kicking, stretching, and even hiccupping as her diaphragm develops, although you can't feel any activity yet. -
Week 12
This week your baby's reflexes kick in: His fingers will soon begin to open and close, toes will curl, and his mouth will make sucking movements. He'll feel it if you gently poke your tummy – though you won't feel his movements yet. -
Week 13
This is the last week of your first trimester. Your baby's tiny fingers now have fingerprints, and her veins and organs are clearly visible through her skin. If you're having a girl, her ovaries contain more than 2 million eggs. -
Week 14
Your baby's brain impulses have begun to fire and he's using his facial muscles. His kidneys are working now, too. If you have an ultrasound, you may even see him sucking his thumb. -
Week 15
Your baby's eyelids are still fused shut, but she can sense light. If you shine a flashlight on your tummy, she'll move away from the beam. Ultrasounds done this week may reveal your baby's sex. -
Week 16
The patterning on your baby's scalp has begun, though the hair isn't visible yet. His legs are more developed – find out when you're likely to feel your baby kick! His head is more upright, and his ears are close to their final position. -
Week 17
Your baby can move her joints, and her skeleton – formerly soft cartilage – is now hardening to bone. The umbilical cord is growing stronger and thicker. -
Week 18
Your baby is flexing his arms and legs, and you may be able to feel those movements. Internally, a protective coating of myelin is forming around his nerves. -
Week 19
Your baby's senses – smell, vision, touch, taste and hearing – are developing and she may be able to hear your voice. Talk, sing or read out loud to her, if you feel like it. -
Week 20
Your baby can swallow now and his digestive system is producing meconium, the dark, sticky goo that he'll pass in his first poop – either in his diaper or in the womb during delivery. -
Week 21
Your baby's movements have gone from flutters to full-on kicks and jabs against the walls of your womb. You may start to notice patterns as you become more familiar with her activity. -
Week 22
Your baby now looks almost like a miniature newborn. Features such as lips and eyebrows are more distinct, but the pigment that will color his eyes isn't present yet. -
Week 23
Your baby's ears are getting better at picking up sounds. After birth, she may recognize some noises outside the womb that she's hearing inside now. -
Week 24
Your baby cuts a pretty long and lean figure, but chubbier times are coming. His skin is still thin and translucent, but that will begin to change soon too. -
Week 25
Your baby's wrinkled skin is starting to fill out with baby fat, making her look more like a newborn. Her hair is beginning to come in, and it has color and texture. -
Week 26
Your baby is now inhaling and exhaling amniotic fluid, which helps develop his lungs. These breathing movements are good practice for that first breath of air at birth. -
Week 27
This is the last week of your second trimester. Your baby now sleeps and wakes on a regular schedule, and her brain is very active. Her lungs aren't fully formed, but they could function outside the womb with medical help. -
Week 28
Your baby's eyesight is developing, which may enable her to sense light filtering in from the outside. She can blink, and her eyelashes have grown in. -
Week 29
Your baby's muscles and lungs are busy getting ready to function in the outside world, and his head is growing to make room for his developing brain. -
Week 30
Your baby is surrounded by a pint and a half of amniotic fluid, although there will be less of it as she grows and claims more space inside your uterus. -
Week 31
Your baby can now turn his head from side to side. A protective layer of fat is accumulating under his skin, filling out his arms and legs. -
Week 32
You're probably gaining about a pound a week. Half of that goes straight to your baby, who will gain one-third to half her birth weight in the next seven weeks in preparation for life outside the womb. -
Week 33
The bones in your baby's skull aren't fused yet. That allows them to shift as his head squeezes through the birth canal. They won't fully fuse until adulthood. -
Week 34
Your baby's central nervous system is maturing, as are her lungs. Babies born between 34 and 37 weeks who have no other health problems usually do well in the long run. -
Week 35
It's getting snug inside your womb! Your baby's kidneys are fully developed, and his liver can process some waste products. -
Week 36
Your baby is gaining about an ounce a day. She's also losing most of the fine down that covered her body, along with the vernix casosa, a waxy substance that was protecting her skin until now. -
Week 37
Your due date is very close, but though your baby looks like a newborn, he isn't quite ready for the outside world. Over the next two weeks his lungs and brain will fully mature. -
Week 38
Are you curious about your baby's eye color? Her irises are not fully pigmented, so if she's born with blue eyes, they could change to a darker color up until she's about a year old. -
Week 39
Your baby's physical development is complete, but he's still busy putting on fat he'll need to help regulate his body temperature in the outside world. -
Week 40
If you're past your due date you may not be as late as you think, especially if you calculated it solely based on the day of your last period. Sometimes women ovulate later than expected. -
Week 41
Your baby is now considered late-term. Going more than two weeks past your due date can put you and your baby at risk for complications, so your provider will probably talk to you about inducing labor.
