The First Trimester

• After a woman has ovulated and the egg has been fertilized, the resulting cell is known as a zygote. The zygote begins immediately to divide at a fast pace and implants itself into the uterus. The baby's hair color, eye color, gender and other physical attributes are determined at this time based solely on hereditary genes passed on to the zygote from the mother's egg and the father's sperm. By your fifth week, or second month, of pregnancy, the zygote becomes a fetus. The baby's organs, such as the heart, and extremities, such as the arms, begin to form, as do the facial features. By the third month, the baby's heart can usually be heard via ultrasound and the fetus is 3 to 4 inches long.
  
  

The Second Trimester

• During the second trimester, a mother can usually feel the fetus beginning to move around. The fetus will develop teeth during the fourth month in the womb, although these teeth will not be visible until many months after the birth. The baby forms a digestive system and starts forming his first stool during the fourth month, and by the fifth month has developed ears. The fetus will also develop eyebrows and eyelashes as well as the ability to suck and swallow in the fifth month. In the sixth month of gestation, the baby will create her own antibodies and reflexes and should weigh between 1 and 1 1/2 lbs.
  
  

The Third and Final Trimester

• By month seven, the baby's bones will be completely developed. He can cry at this point and should be very active. The eighth month is spent growing, and the baby will have periods of deep sleep, but should still be relatively active. By this point, the baby is almost fully developed and almost ready for life outside of the womb. The baby should be head-down in the womb and, after nine months of gestation and development, the expectant mother should give birth to a fully developed baby weighing 6 to 11 lbs., 7 to 8 lbs. being the average.