Trust me, you will know when they are pregnant. I myself asked the same question "how can I tell?" and people were laughing and just saying "you'll know, trust me, you'll know". And that is true, they look like they have swallowed a golf ball when they got about a week, a week and a half to go. When they are ready to blow I barely dare to touch them I feel like it could be a "tooth paste accident" if you know what I mean