Trimester by Trimester

First Trimester

Here's a month-by-month guide to your baby's development:

Month 1

• Tiny limb buds, which will grow into arms and legs, appear.
• The embryo looks like a tadpole.
• The heart and lungs begin to form. By the 25th day, the heart starts to beat.
• The neural tube, which becomes the brain and spinal cord, begins to form.
• At the end of the first month, the embryo is about 1/2 inch long and weighs less than 1 ounce.

Month 2

• All major body organs and systems are formed but not completely developed.
• The early stages of the placenta, which exchanges nutrients from your body for waste products produced by the baby, are visible and working.
• The ears, ankles, and wrists form. The eyelids form and grow but are sealed shut.
• Fingers and toes develop.
• By the end of the second month, the fetus looks more like a person than like a tadpole, is about 1 inch long and still weighs less than 1 ounce.

Month 3

• After 8 weeks as an embryo, the baby now is called a "fetus."
• The fingers and toes have soft nails.
• The mouth has 20 buds that will become "baby teeth."
• You can hear your baby's heartbeat for the first time (10 to 12 weeks) using a special instrument called a Doptone.
• For the rest of pregnancy, the body organs will mature, and the fetus will gain weight.
• By the end of this month, the fetus is 2 1/2 inches long and weighs a little over 1 ounce.