These would be great questions to ask a doctor.

They test you for as many that will show up on a blood test as far as I know and the reason why is that they can be passed on to the child either during pregnancy or while giving birth and some of these can be life threatening for a baby

As far as I know they do. An std could be harmful during pregnancy and should be treated when necessary.

I work in a hospital and I am around ob patients all day long....When it comes to stds during pregnancy providers/doctors are very careful....It is very important not to have any stds such as hiv and syphylus<---sorry about the spelling....They also check for ghonorrhea and chlamydia and hepatitis....All of these can be passed to your baby during pregnancy or can cause all sorts of problems for you....But you can choose not to have the tests done most of the time....But doctors will try to presuade you to do so....Plus wouldnt you rather know that you have an std.....Rather than having one and passing it to your spouse or sexual partner?