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.
For more resources on pregnancy click here.