My OB said that too. So, I went for the dental cleaning at the 5th month of pregnancy. Once you tell them the pregnancy, they will be very careful. After the birth, I went for cleaning again. Because of the breastfeeding, the gum swelled a bit. So, the hygienist was very careful to prevent too much bleeding.
It should be fine. Any concerns you have, discuss them with the hygienist. They should have much experience to address your concerns.