You cannot know for certain how many babies a guinea pig is expecting before she gives birth. Here is why:
* Ultrasound and X-rays are rarely used on pregnant guinea pigs because they can be invasive and risky.
* The gestation period lasts only about 63 days, leaving little time to estimate litter size from belly changes.
* Litter sizes vary widely, from 1 to 10 babies, with an average of 4–6.
As the due date nears, you may notice her belly growing and her behavior shifting, but these are not reliable indicators of exact numbers. The best approach is patience and preparation for the arrival of the pups.