• The fertilized egg is called an embryo at this stage.
• The head has formed and buds begin to grow at the limbs forlegs and arms.
• The heart and lungs are the first organs to form, and by the 25th day the heart will start to beat.
• The brain and spinal cord begin to form as the neural tube.
• The embryo weighs less than one ounce and is approximately .014 inches long by the end of Week 4.

A standard staple is approximately 0.014 inches thick

Click here for a list of clinics offering free pre-natal ultrasounds