Pregnant women are susceptible to develop periodontitis, but these oral health changes related to pregnancy are often neglected. Periodontitis is accompanied by a low-grade systemic inflammation and can be harmful to the general health of the woman, contribute to pre-term birth and adversely influence the future health and metabolism of the offspring. Despite this, studies indicate that 40% of Danish women in childbearing age do not visit a dentist regularly. The PROBE controlled intervention study will investigate the beneficial effect of treatment of periodontal disease during pregnancy on fetal growth, preterm delivery and birth weight.