In this Article

• Introduction
• What is the first trimester (week 1-week 12)?
• What is the second trimester (week 13-week 28)?
• What is the third trimester (week 29-week 40)?
• How will my baby develop week by week?
• What are the changes that happen to a woman's body during her 1st, 2nd, and 3rd trimesters of pregnancy?
• Body aches
• Breast changes
• Constipation
• Dizziness
• Fatigue, sleep problems
• Heartburn and indigestion
• Hemorrhoids
• Itching
• Leg cramps
• Morning sickness
• Nasal problems
• Numb or tingling hands
• Stretch marks, skin changes
• Swelling
• Urinary frequency and leaking
• Varicose veins
• Stages of Pregnancy - Slideshow
• Patient Discussions: Pregnancy - Describe Your Experience
• Pregnancy Glossary
• Pregnancy Index

How will my baby develop week by week?

First Trimester (week 1-week 12)

At 4 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 1/25 of an inch long.

At 8 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 8 weeks, your baby is a fetus and looks more like a human. Your baby is nearly 1 inch long and weighs less than 1/8 of an 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.

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.

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 ½ 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.

Pregnancy - Describe Your Experience

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