How do you find out if you are pregnant on second life

You cannot "find out". You must choose to be pregnant.

Since your avatar cannot actually become pregnant like in real life, you must choose or "role play" that your avatar is pregnant. This means that you either decide to role-play that you are pregnant and pretend that you are, or you use a script or service to simulate the pregnancy. Services and scripts for this are available in-world, usually for a fee or charge.