Ideally, if you're planning to get pregnant, having dental check-ups/consultations is really recommended. Why??Pregnancy has a big effect in your dental health and vice versa.  In this way, we can do aggressive treatments if deemed necessary without harming the mother and the baby. Just like in cases of Chronic Periapical Periodontis or severely decayed tooth which needs tooth extraction. Also in cases of impacted wisdom tooth which also needs to be removed especially if it has forming cyst surrounding it. This cases, if left untreated can get worst and can lead to cellulitis or Ludwig's angina which is life threatening, and we all know that pregnant women has lower immune system than normal people do, so imagine how fast  bacterias and viruses can spread during pregnancy. Pathogens tend to get opportunistic when we have lower defense cells in our body. 

This kind of infections need an aggressive treatment: a massive dose of antibiotic (broad spectrum) through IV, and removal of the cause (surgical procedure). And this must be coordinated and planned with your OB.