Can you ring the gyno and check with them? I wouldn't neccessarily have another one now unless there was a need. It's possible that the letter was sent prematurely. Yes, it's important to have them regularly, but if you are not due for another 6 months, i personally wouldn't be rushing to have it done now.

However, if i was TTC i would probably get the smear down first so i didn't have to worry during the pregnancy.