We often see cases where guinea pigs have been incorrectly identified as the wrong sex. A common scenario is when someone purchases two guinea pigs and are told they are two males or females. A month or so later they go to check the guinea pigs and find that all of a sudden there is a heap of babies running around! They then bring the guinea pigs in for us to check and we see that they actually had a male and a female that are now proud parents!