Guinea pigs mate early and often, so when kept as pets, they should be separated according to sex. Otherwise, you'll be left with the pitter patter of little paws. If your guinea pig does get pregnant, though, the stages of her pregnancy are relatively predictable and consistent, so you always can know what to expect from her and her pups.
A female guinea pig goes into estrus three or four times every year, giving her and her mate plenty of opportunities to breed. She starts estrus when she's just older than two months, so don't be surprised if a relatively young pet gets pregnant. Males choose their mates by smelling them, then marking them with urine. While the female is in estrus, he mates with her overnight, making her pregnant.
Guinea pig pregnancy is relatively short, lasting only between 59 and 72 days. The average duration of a pregnancy is 65 days, but it depends on how many pups she is carrying -- her pregnancy will be shorter if she's carrying more pups. An average littler is three or four pups, which is enough for a guinea pig to become noticeably bigger during the pregnancy. A veterinarian can determine how many babies she is carrying, ensuring that she delivers all of them successfully.
Once she goes into labor, the birthing process shouldn't take long -- only about 30 minutes or so. If your guinea pig takes longer than this or shows signs of struggling, she may need immediate veterinary attention, as they sometimes require assistance giving birth. The pups are born relatively well-developed, with teeth, hair, open ears and open eyes.
Guinea pig pups eat solid food from birth, but they also get nutrition from their mother. About 5-8 days after giving birth, the mother begins lactating for her pups, but they don't rely on her for long. After only two or three weeks since their birth, the pups are weaned and become independent. Be mindful of her behavior after birth, as guinea pigs won't hesitate to become pregnant again right away.
Tom Ryan is a freelance writer, editor and English tutor. He graduated from the University of Pittsburgh with a degree in English writing, and has also worked as an arts and entertainment reporter with "The Pitt News" and a public relations and advertising copywriter with the Carnegie Library of Pittsburgh.