Always inform your dentist that you are pregnant, so they can take the necessary precautions. 
Routine clean ups are fine, but avoid any treatments especially non-essential cosmetic dentistry, in the first trimester and the latter  half of the third. Avoid dental X rays altogether when you’re expecting.
Women are more susceptible to certain dental problems like periodontal disease while pregnant, so gum exams are important. Besides this, regular flossing and good oral care at home will ensure you steer clear of any pregnancy related dental issues. Keep an eye out for any changes in your gums that could be a result of hormonal changes. If something seems amiss, schedule a visit with your dentist right away.