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Home > A-Z Health Topics > Pregnancy > You're pregnant: Now what? > Stages of pregnancy

Stages of pregnancy

• First trimester (week 1-week 12)
• Second trimester (week 13-week 28)
• Third trimester (week 29-week 40)
• Your developing baby
• More information on stages of pregnancy

Pregnancy lasts about 40 weeks, counting from the first day of your last normal period. The weeks are grouped into three trimesters (TREYE-mess-turs). Find out what's happening with you and your baby in these three stages.

First trimester (week 1-week 12)

First trimester

See how your baby is growing inside of you during the first trimester.

Did you know?

For some women, body image is a huge concern during pregnancy. Learn what you can do to accept and love your pregnant body in our Pregnancy and body image section.

During the first trimester your body undergoes many changes. Hormonal changes affect almost every organ system in your body. These changes can trigger symptoms even in the very first weeks of pregnancy. Your period stopping is a clear sign that you are pregnant. Other changes may include:

• Extreme tiredness
• Tender, swollen breasts. Your nipples might also stick out.
• Upset stomach with or without throwing up (morning sickness)
• Cravings or distaste for certain foods
• Mood swings
• Constipation (trouble having bowel movements)
• Need to pass urine more often
• Headache
• Heartburn
• Weight gain or loss

As your body changes, you might need to make changes to your daily routine, such as going to bed earlier or eating frequent, small meals. Fortunately, most of these discomforts will go away as your pregnancy progresses. And some women might not feel any discomfort at all! If you have been pregnant before, you might feel differently this time around. Just as each woman is different, so is each pregnancy.

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Second trimester (week 13-week 28)

Second trimester

See how your baby is growing inside of you during the second trimester.

Did you know?

You can do something about common pregnancy discomforts. Learn more.

Most women find the second trimester of pregnancy easier than the first. But it is just as important to stay informed about your pregnancy during these months.

You might notice that symptoms like nausea and fatigue are going away. But other new, more noticeable changes to your body are now happening. Your abdomen will expand as the baby continues to grow. And before this trimester is over, you will feel your baby beginning to move!

As your body changes to make room for your growing baby, you may have:

• Body aches, such as back, abdomen, groin, or thigh pain
• Stretch marks on your abdomen, breasts, thighs, or buttocks
• Darkening of the skin around your nipples
• A line on the skin running from belly button to pubic hairline
• Patches of darker skin, usually over the cheeks, forehead, nose, or upper lip. Patches often match on both sides of the face. This is sometimes called the mask of pregnancy.
• Numb or tingling hands, called carpal tunnel syndrome
• Itching on the abdomen, palms, and soles of the feet. (Call your doctor if you have nausea, loss of appetite, vomiting, jaundice or fatigue combined with itching. These can be signs of a serious liver problem.)
• Swelling of the ankles, fingers, and face. (If you notice any sudden or extreme swelling or if you gain a lot of weight really quickly, call your doctor right away. This could be a sign of preeclampsia.)

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Third trimester (week 29-week 40)

Third trimester

See how your baby is growing inside of you during the third trimester.

You're in the home stretch! Some of the same discomforts you had in your second trimester will continue. Plus, many women find breathing difficult and notice they have to go to the bathroom even more often. This is because the baby is getting bigger and it is putting more pressure on your organs. Don't worry, your baby is fine and these problems will lessen once you give birth.

Some new body changes you might notice in the third trimester include:

• Shortness of breath
• Heartburn
• Swelling of the ankles, fingers, and face. (If you notice any sudden or extreme swelling or if you gain a lot of weight really quickly, call your doctor right away. This could be a sign of preeclampsia.)
• Hemorrhoids
• Tender breasts, which may leak a watery pre-milk called colostrum (kuh-LOSS-struhm)
• Your belly button may stick out
• Trouble sleeping
• The baby "dropping", or moving lower in your abdomen
• Contractions, which can be a sign of real or false labor

As you near your due date, your cervix becomes thinner and softer (called effacing). This is a normal, natural process that helps the birth canal (vagina) to open during the birthing process. Your doctor will check your progress with a vaginal exam as you near your due date. Get excited — the final countdown has begun!

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Your developing baby

First trimester (week 1-week 12)

	At four weeks: Your baby's brain and spinal cord have begun to form. The heart begins to form. Arm and leg buds appear. Your baby is now an embryo and one-twenty-fifth inch long.
	At eight weeks: All major organs and external body structures have begun to form. Your baby's heart beats with a regular rhythm. The arms and legs grow longer, and fingers and toes have begun to form. The sex organs begin to form. The eyes have moved forward on the face and eyelids have formed. The umbilical cord is clearly visible. At the end of eight weeks, your baby is a fetus and looks more like a human. Your baby is nearly 1 inch long and weighs less than one-eighth ounce.
	At 12 weeks: The nerves and muscles begin to work together. Your baby can make a fist. The external sex organs show if your baby is a boy or girl. A woman who has an ultrasound in the second trimester or later might be able to find out the baby's sex. Eyelids close to protect the developing eyes. They will not open again until the 28th week. Head growth has slowed, and your baby is much longer. Now, at about 3 inches long, your baby weighs almost an ounce.

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Second trimester (week 13-week 28)

	At 16 weeks: Muscle tissue and bone continue to form, creating a more complete skeleton. Skin begins to form. You can nearly see through it. Meconium (mih-KOH-nee-uhm) develops in your baby's intestinal tract. This will be your baby's first bowel movement. Your baby makes sucking motions with the mouth (sucking reflex). Your baby reaches a length of about 4 to 5 inches and weighs almost 3 ounces.
	At 20 weeks: Your baby is more active. You might feel slight fluttering. Your baby is covered by fine, downy hair called lanugo (luh-NOO-goh) and a waxy coating called vernix. This protects the forming skin underneath. Eyebrows, eyelashes, fingernails, and toenails have formed. Your baby can even scratch itself. Your baby can hear and swallow. Now halfway through your pregnancy, your baby is about 6 inches long and weighs about 9 ounces.
	At 24 weeks: Bone marrow begins to make blood cells. Taste buds form on your baby's tongue. Footprints and fingerprints have formed. Real hair begins to grow on your baby's head. The lungs are formed, but do not work. The hand and startle reflex develop. Your baby sleeps and wakes regularly. If your baby is a boy, his testicles begin to move from the abdomen into the scrotum. If your baby is a girl, her uterus and ovaries are in place, and a lifetime supply of eggs have formed in the ovaries. Your baby stores fat and has gained quite a bit of weight. Now at about 12 inches long, your baby weighs about 1½ pounds.

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Third trimester (week 29-week 40)

	At 32 weeks: Your baby's bones are fully formed, but still soft. Your baby's kicks and jabs are forceful. The eyes can open and close and sense changes in light. Lungs are not fully formed, but practice "breathing" movements occur. Your baby's body begins to store vital minerals, such as iron and calcium. Lanugo begins to fall off. Your baby is gaining weight quickly, about one-half pound a week. Now, your baby is about 15 to 17 inches long and weighs about 4 to 4½ pounds.
	At 36 weeks: The protective waxy coating called vernix gets thicker. Body fat increases. Your baby is getting bigger and bigger and has less space to move around. Movements are less forceful, but you will feel stretches and wiggles. Your baby is about 16 to 19 inches long and weighs about 6 to 6½ pounds.
	Weeks 37-40: By the end of 37 weeks, your baby is considered full term. Your baby's organs are ready to function on their own. As you near your due date, your baby may turn into a head-down position for birth. Most babies "present" head down. At birth, your baby may weigh somewhere between 6 pounds 2 ounces and 9 pounds 2 ounces and be 19 to 21 inches long. Most full-term babies fall within these ranges. But healthy babies come in many different sizes.

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More information on stages of pregnancy

Explore other publications and websites

• First Trimester Pregnancy: What to Expect (Copyright © Mayo Foundation) — This fact sheet discusses the physical changes and symptoms experienced in the first three months of pregnancy.
  http://www.mayoclinic.com/health/pregnancy/PR00004
• How Your Baby Grows (Copyright © March of Dimes) — This site provides information on the development of your baby and the changes in your body during each month of pregnancy. In addition, for each month, it provides information on when to go for prenatal care appointments and general tips to take care of yourself and your baby.
  http://www.marchofdimes.com/pnhec/28699_2134.asp
• Morning Sickness (Copyright © American Academy of Family Physicians) — This publication discusses morning sickness, how long it will last, and how to help relieve the symptoms.
  http://familydoctor.org/online/famdocen/home/women/pregnancy/basics/154.html
• Pregnancy Calendar: A Week-by-Week Guide (Copyright © Nemours Foundation) — This illustrated pregnancy calendar is a detailed guide to all the changes taking place in your baby — and in you! Each week of pregnancy includes a description of your baby's development, as well as an explanation of the changes taking place in your body. You'll also find important medical information that will help keep you and your baby healthy.
  http://www.kidshealth.org/parent/pregnancy_newborn/calendar/pregnancy_calendar_intro.html
• Second Trimester Pregnancy: What to Expect (Copyright © Mayo Foundation) — This fact sheet discusses how the changes that began in the first weeks of pregnancy increase and accelerate during the second trimester. Of these, your growing uterus is probably the most obvious. But many other, unseen events are also taking place.
  http://www.mayoclinic.com/print/pregnancy/PR00018/METHOD=print
• Taking Care of You and Your Baby While You're Pregnant (Copyright © American Academy of Family Physicians) — This publication discusses the importance of prenatal care, what happens during doctor visits, how much weight should be gained during pregnancy, what you should eat, and also a list of dos and don’ts during pregnancy.
  http://familydoctor.org/online/famdocen/home/women/pregnancy/basics/053.html
• Third Trimester Pregnancy: What to Expect (Copyright © Mayo Foundation) — This fact sheet explains how at term or the third trimester, the uterus will weigh about 2 1/2 pounds and will have stretched to hold your baby, the placenta, and about a quart of amniotic fluid. Nearly all of the physical symptoms of late pregnancy arise from this increase in the size of the uterus.
  http://www.mayoclinic.com/print/pregnancy/PR00009/METHOD=print
• Weight Gain During Pregnancy (Copyright © March of Dimes) — This brief fact sheet explains how much weight a woman should gain during pregnancy by explaining the different aspects of pregnancy that add to overall weight.
  http://www.marchofdimes.com/printableArticles/159_153.asp

Connect with other organizations

• American Academy of Family Physicians
  http://familydoctor.org/online/famdocen/home.html
• American College of Obstetricians and Gynecologists
  http://www.acog.org/
• American Pregnancy Association
  http://www.americanpregnancy.org/
• KidsHealth
  http://kidshealth.org/
• March of Dimes
  http://www.marchofdimes.com

Content last updated September 27, 2010.

Resources last updated September 27, 2010.

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