If your female guinea pig was exposed to a male guinea pig, whether by accident or intentional breeding, you may be curious to know if she is pregnant. Unfortunately there are no pregnancy test strips for guinea pigs. However, there are a few methods you can use to determine if your guinea pig is expecting pups.
Note your guinea pig's behaviour. According to the Guinea Pig Resource website, a non-pregnant female guinea pig becomes fertile every 16 days, demonstrating behavioural changes such as "mounting cage mates, growling, and lifting her rear end into mating position when touched." If these behaviours are absent 16 days after the female was bred and beyond, she is likely pregnant.
Weigh your guinea pig with a kitchen scale on a weekly basis and note any changes. If she is gaining weight steadily, this may be a sign that she is pregnant. Some guinea pigs will double their weight while pregnant. You may also notice her abdomen becoming larger. However, weight gain can also be attributed to diet (if you are feeding her too much or using a feed too high in calories) or age (if your guinea pig has not yet reached adulthood).
Observe her eating habits. If your guinea pig is expecting pups, her appetite will probably increase as she gets further along in her pregnancy.
Watch her abdomen for movements and place your hands on either side of her to check for any noticeable kicks. Guinea pigs usually have one to six offspring per litter, with three or four being the average. By the seventh week of pregnancy, you may be able to see or feel the pups moving, which is a solid indication that a litter of baby guinea pigs is on the way. The average gestation for guinea pigs is 63 days.