Pregnancy Timeline

Weeks 1 and 2
Congratulations, you're pregnant! You may not know it yet, though. Many women do not learn that they are pregnant until they are four or five weeks along. Signs that you may be pregnant include missing your period, nausea, food aversions and cravings, frequent trips to the bathroom, excessive tiredness and breast tenderness.
Week 3
Right now your baby is a group of cells, growing rapidly. You probably don't know you're pregnant yet, since you most likely haven't missed your period.
Week 4
Your pregnancy still isn't showing, as your baby is only 1mm long. You will likely miss your period at the end of this week, which may be the first tip-off that you're pregnant. Right now the amniotic cavity, which will hold the amniotic fluid, is starting to form, as is the placenta. Layers of cells are developing that will eventually become the nervous system, the gastrointestinal tract, liver, pancreas, thyroid, skeleton, connective tissue, blood system, urogenital system and muscles.
Week 5
Your baby is about .05 inches long and you still aren't showing. A home pregnancy test may show that you are pregnant. The baby's brain and spinal cord (also known as the central nervous system) are starting to take shape.
You may start experiencing morning sickness around now, which is nausea that can actually occur any time of day. To fend off morning sickness, try eating small, frequent meals and avoiding sweets. Talk to your doctor if your morning sickness seems excessive.
Week 6
Your baby is approximately .08 to .16 inches long. Your baby is measured from crown to rump (the top of the head to the buttocks). This is because it can be too difficult to measure a baby's bent legs.
You may have noticed a change in your weight, although if this is your first pregnancy, it is unlikely that anyone else has. You may have gained a little bit of weight, or even lost some if you've had trouble eating due to morning sickness. You may also start experiencing heartburn, which is caused by gastric and duodenal contents backing up into the esophagus. You may also get constipation, a common complaint during pregnancy.
The baby's neural groove closes during this week and early brain chambers form. Eyes and limb buds will start to appear now. Your doctor may be able to find the baby's heartbeat on an ultrasound.
Week 7
Your baby is 4 to 5mm long now. You may have gained weight, but probably still won't be showing. Leg and arm buds are becoming more pronounced, with the arm buds dividing into hand and arm-shoulder segments. The baby's heart has divided into right and left chambers, intestines are developing and the appendix and pancreas are present.
Week 8
Your baby is ½ to ¾ of an inch long this week. You may have some sciatic-nerve pain, which radiates through your buttocks and down the back or side of your legs. There is not much you can do to avoid this pain, except trying to lay in different positions.
Your baby's eyelids are beginning to form and the nose is just barely visible. Ears are also forming, and arms are longer and bend. Toes are just beginning to grow on your baby's feet.
Week 9
Your baby starts moving this week. The baby is 1 to 1 ¼ inches this week and the arms and legs are getting longer. Hands meet over the heart and feet can almost reach each other. Eyelids almost cover the eyes.
Week 10
Your baby may be up to 1 ¾ inches by now. This marks the end of the embryonic period and the beginning of the fetal period. Most congenital defects will have occurred by now.
You may be feeling a bit bigger this week and also notice that you are emotional. This may be because of hormonal changes, but remember that it's completely normal.
Week 11
Your baby is 1 ½ inches to 2 ½ inches long. The fetus will start growing very quickly, doubling in length over the next three weeks. The head will make up nearly half of this length. Your baby is also developing fingernails.
You may be noticing that you're losing hair or even growing more. Fingernails and hair sometimes grow more quickly during pregnancy. Most of the excess hair will fall out after you deliver the baby.
Week 12
Your baby is growing quickly now. You may be able to hear your baby's heartbeat this week. Fingers and toes have separated by this point and you may soon be able to tell if you're having a boy or a girl. Morning sickness may be getting better for you by now. You might feel as though your clothes are getting too tight, especially if this isn't your first pregnancy.
Week 13
By now you can measure your baby in weight, which this week is between ½ and ¾ of an ounce. Your baby's body will start to catch up in size to the head, and the face begins to look human.
You may be noticing stretch marks now, although they might not come until later. Some say that stretch marks are inevitable if you are predisposed for them. Steady weight gain and regularly rubbing cocoa butter on your stomach may help to prevent them.
Week 14
Your baby weighs just about an ounce and the ears have moved to the side of the head. Eyes are moving to the front of the face.
You are probably in maternity clothes by now, or getting close as your body grows. You may be noticing skin tags, which are elongated bumps of skin that may appear or grow during pregnancy.
Week 15
Your baby weighs almost 1 ¾ ounces. Lanugo hair, which is fine hair, covers your baby's body now. Thumb sucking often begins around this time.
Sleeping is probably starting to become difficult because of your body. Try pillows between your legs and at your sides to keep you comfortable.
Week 16
Your baby is a little over four inches long and weighs 2 ¾ ounces. You may be able to feel your baby move. It could feel like gas or popcorn popping. Soon you'll get used to the feeling.
Week 17
This week your baby is 4 ½ to 4 ¾ inches long and weighs about 3 ½ ounces. Fat starts forming this week on your baby.
You may be feeling slight pain as your uterus grows, called round-ligament pain. Talk to your doctor is the pain is severe or you have other symptoms, such as bleeding or discharge.
Week 18
Your baby may be up to 5 ½ inches this week and weigh 5 ¼ ounces. An ultrasound may be able to detect heart defects at this point.
You probably have back pain as your stomach grows. Exercise and sleeping on your side may help.
Week 19
Your baby weighs about 7 ounces and is up to 6 inches long. Your baby is continuing to grow and develop.
You may be experiencing low blood pressure, which can cause you to feel dizzy when you stand or move suddenly.
Week 20
You're halfway there! By now your baby is 5 2/3 to 6 ½ inches long and weighs roughly 9 ounces. An ultrasound may be able to determine the sex of your baby, if you want to know.
Week 21
Your baby is up to 7 ¼ inches and weighs about 10 ½ ounces. Your baby's growth is slowing down, even as it continues to develop. By this week your baby is able to swallow amniotic fluid, which allows it to absorb the water and pass the unabsorbed matter to the large bowel.
Week 22
Your baby is about 7 2/3 inches and weighs 12 ¼ ounces. Your baby's eyelids and eyebrows are almost fully developed and fingernails cover the fingertips.
Watch out for anemia while you're pregnant; the iron deficiency can leave you feeling tired and pregnant women are especially susceptible to it. Talk to your doctor about taking prenatal supplements if your energy level starts to crash.
Weeks 23 and 24
Your baby is about 1 to 1 ¼ pounds and 8 to 8 ½ inches. The baby's face will become more defined and the pancreas is developing.
You may be feeling even more emotional now, which is completely normal. It should subside after delivery.
Weeks 25 and 26
Your baby is now between 1 ½ and 2 pounds. By week 25, if your baby were born early, there would have a chance at survival.
Your skin may start itching now. Try not to scratch where it itches, as that can make it worse.
Weeks 27 and 28
Week 27 marks the beginning of the third trimester. Your baby now weighs between 2 and 2 ½ pounds and is about 9 2/3 inches long. The eyelids are able to open now, and the retina has developed.
Weeks 29 and 30
Now your baby weighs between 2 ¾ and 3 pounds and is between 10 ½ and 10 ¾ inches. If delivered now, your baby would still be considered preterm but would have a better chance of survival.
Should you be at risk for preterm delivery, you may be confined to bed rest. Laying on your side is best. There are also some medications your doctor may prescribe if it seems you may go into labor too early.
Weeks 31 and 32
Your baby weighs between 3 ½ to 4 pounds and is more than 11 ½ inches long. Your baby is continuing to grow, preparing for its entrance to the world.
You may notice swelling in your legs and feet now, which is due to your body producing 50% more blood and body fluids than usual. At week 32 you will probably start seeing your doctor every 2 weeks.
Weeks 33 and 34
Your baby weighs between 4 ½ and 5 pounds and is more than a foot long. Its crown to toe length is almost 19 ½ inches. The baby may drop soon, which means that the baby's head enters the birth canal.
You may notice that you're gaining weight more quickly than during earlier weeks of pregnancy. This is because the baby is going through a growth spurt and may be growing up to ½ pound each week. Heartburn may be worse now because your stomach doesn't have as much room for digestion.
Weeks 35 and 36
Your baby weighs between 5 ½ and 6 pounds and is more than 13 ¼ inches long from crown to rump. Your baby's lungs and respiratory system have begun the final stages of development.
You may be very uncomfortable right now. Your size can make everything difficult to do, and hormones are making you very emotional and irritable.
Weeks 37 and 38
Your baby is between 6 ½ and 6 ¾ pounds and is about 14 inches long from crown to rump. The baby's total length is roughly 21 inches. Your baby is still growing and will continue until delivery.
It's a good idea to become familiar with postpartum depression now, as you may experience it after the baby is born. Rest assured that it is completely normal, and with treatment you can be back to feeling like your old self again.
Weeks 39 and 40
Your baby is a little over 7 pounds now, and has grown about ½ to 1 inch longer. The baby is fully developed now and simply waiting for its time to arrive.