Pregnant Dog Cycle

Dog is catchall term applied to one of hundreds of varieties of carnivorous, domesticated mammals, scientifically classified as the species Canis familiaris or Canis lupus familiaris. Depending on the authority, dogs are either considered a species of wolf or closely related to wolves, and were domesticated 10,000 to 14,000 years ago. A dog's pregnancy or gestation period lasts 50 to 70 days, with puppy litters ranging from one to 10.

  1. Conception

    • Dogs engage in sexual reproduction. Female dogs, also called bitches, only mate during estrus -- or when the animals are in heat. This period lasts up to 22 days, approximately every six months. Upon conception, a female's eggs are fertilized in the oviducts.

    First Trimester

    • During the first week of a dog's pregnancy, changes begin to occur within the dog's system; however, no outward signs of gestation are evident. The eggs are transformed into blastocysts, and eventually embryos, during the second week. Physical changes begin to take place during the third week, when the dog's nipples become darker and larger, and by week's end, the dog's stomach fur becomes thinner.

    Second Trimester

    • The second trimester begins with the fourth week. The reason is that in any organism, trimesters are basically three evenly divided time phases within a pregnancy. So, unlike humans, who have a total of three, three-month trimesters to correspond with a nine-month gestation period, a dog has three, three-week trimesters to correspond with a 50- to 70-week gestation period. During the second trimester, the dog may begin to experience morning sickness. During the fifth week, the dog's stomach begins to swell. These events continue through the sixth week. By the end of the second trimester, the dog's stomach will be larger and its appetite wanes.

    Third Trimester

    • Week seven ushers in the third trimester. A dog's normal rectal temperature during pregnancy is about 101 degrees. During this final trimester, the temperature drops to 98 degrees when labor and delivery is within 12 to 24 hours. Whelping is the process that a dog goes through behaviorally and physically before and during labor and delivery. A marked restlessness and need for seclusion begins, as the uterus progressively enlarges.

    Labor and Delivery

    • A dog's labor and delivery can be divided into three stages. The first stage of labor can last six to 24 hours. During that time, the dog's restlessness or nervousness becomes more extreme. Upon stage two, contractions begin and a greenish, fluid sac begins to protrude from the dog's vulva. The puppy soon follows, attached to its placenta. Puppies are usually delivered nose first, with their stomachs down; however, approximately one-third of deliveries occur with a puppy's hindquarters exiting first. Stage three is a resting phase. Afterbirth substances are expelled with mild contractions. Depending on the dog, stage three can last from several seconds to a couple hours.