Mating

• Every once in a while (about three times a year), an unspayed female cat will go into heat. This is the time she is fertile, and she will actively seek out a male cat with which to mate.
  
  Heat cycles last for about a week, and they are noticeable to humans by a few signs. Although there is a slight discharge of blood, it is not nearly as noticeable as it is in dogs, so this sign is often missed. Cats in heat also often become much more affectionate toward their owners, and will continuously sound out a loud meowing to let males in the area know that they are available for mating.
  
  If a female mates in this time, the chances are very good that she will become pregnant.
  
  

Growth

• After the fertilized eggs implant at about two weeks after mating, the fetuses begin to grow. They develop organs first, and after about a month they are recognizably kittens. For the remainder of the pregnancy, the fetuses will simply grow larger and stronger, becoming capable of life outside the womb.
  
  A cat's pregnancy lasts about two months, during which the fetuses will become completely developed.
  
  

Changes in Mother

• The mother cat goes through many visible changes through the course of her pregnancy. One of the most noticeable is that her nipples will drastically change in color and size. They will turn pink and become much larger, starting at about the third week of pregnancy.
  
  Like humans, cats often need much more sleep when pregnant, and they take naps more often. Another similarity to human pregnancy--pregnant cats might throw up more often, or they might refuse food because of nausea.
  
  

Detection

• Pregnancy stages in cats can be detected easily by a veterinarian. The veterinarian or technician can use use an ultrasound device to determine whether a cat who has been showing symptoms is pregnant. This ultrasound can often also allow a vet to count the number of kittens the cat will have. If the cat is brought in a few weeks later in the pregnancy, the vet might not have to use the ultrasound at all, but can instead simple feel the developing kittens through the mother's skin.
  
  

Birth

• About two months after mating (give or take a few days), a cat will be ready to give birth. Often owners will not interfere in a cat's birth unless it is very obvious that something has gone wrong; otherwise, cats are able to give birth on their own independently.
  
  When a cat is about to give birth, there is a red or yellow discharge. This means that labor has begun. The birth of the first kitten can take anywhere from a few minutes to a few hours. After that, the other kittens will be about an hour apart.
  
  After delivery, the cat will chew through the umbilical cord and begin caring for her kittens.