Division of Baby Development

• The development of a baby occurs over the course of 280 days. This period of time is divided up into three trimesters. The first trimester consists of the first through third months, the second trimester consists of the fourth through sixth months, and the third trimester occurs during the seventh to ninth months.
  
  

First Trimester

• At one month, your baby is considered an embryo. The baby has two layers of cells, and it is from these cells that her organs and body parts will develop.
  
  In the second month, your baby has grown to approximately 1.10 to 1.18 inches, or 28 to 30 millimeters. The baby is moving around now, although you can't feel anything yet. Each finger can be clearly seen, and they are slightly webbed.
  
  Your three-inch long baby weighs nearly 1 oz. by the third month. The fingerprints that are unique only to this particular baby have developed by now.
  
  

Second Trimester

• The fourth month starts the second trimester, and the embryo has now become a fetus. Additionally, the baby is approximately five inches long and weighs about 5 oz.. Hardening of the skeleton, from cartilage with a rubbery feel, to bone, has begun.
  
  If your baby was stretched out fully at the beginning of the fifth month, the baby's length would be more than 10 inches. The baby's eyebrows and eyelids have developed. Weight is at about a pound and a half now that your baby has entered the sixth month. The baby fat is starting to smooth out skin that before had been wrinkled.
  
  

Third Trimester

• The seventh month is the beginning of the third trimester, and the more than 15-inch long baby is weighing about three pounds. The baby's eyes can open and close and will follow a light that is moved back and forth.
  
  In the eight month, the baby weighs about 4 ¾ pounds. The baby is becoming rounder as fat layers continue to be laid down, and the lungs are well-developed.
  
  By the ninth month, if the baby is of average weight and length, the weight will be approximately seven pounds, and the length will be more than 19 inches. However, there are wide variations at this stage.