If the patient does not have severe periodontitis per se and the oral problem is only discovered because of pregnancy, it is usually the result of altered sex hormone levels during pregnancy that exacerbates periodontitis and turns periodontal inflammation that was already present in the mouth from inconspicuous to obvious.
The gums are the target tissue for female hormones and during pregnancy sex hormone levels increase and inflammation is exacerbated by increased exudation of inflammatory cells. If not treated accordingly to control the inflammation, the inflammation continues to progress and the alveolar bone is destroyed, leading to gum recession and exposed roots.