Tracking Your Baby's Growth During Your Pregnancy

Fetus Development
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.
Fetus Development
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 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.
Fetus Development
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.
Fetus Development
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.
Fetus Development
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.
Fetus Development
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.
Fetus Development
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.
Fetus Development
At 37-40 Weeks
  • 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.

Source: “Stages of Pregnancy” WomensHealth.gov.
Content last updated September 27, 2010.