Ka Hung Chan, Derrick Bennett, Kin Bong Hubert Lam and Zhengming Chen
Chronic liver diseases (CLD), such as liver cirrhosis and liver cancer, affect more than 800 million people worldwide, with a third of these living in China. Smoke from solid fuels (e.g. coal and wood) and tobacco contains high concentrations of thousands of toxic chemicals. When breathed in, these chemicals can reach and harm major internal organs, including the liver.
The Obstetrics and Periodontal Therapy (OPT) Study was an NIH-funded randomised controlled trial designed to evaluate whether periodontal treatment in pregnant women had any effect on preterm birth; its findings were published in 2006. The investigators randomly assigned about 800 women who had been pregnant for less than 16 weeks, and had periodontal disease, to one of two groups. One group received periodontal treatment during pregnancy, whereas the other group received treatment after pregnancy.
Although the study found that treatment controlled periodontal infection and reduced the microorganism load, there was no difference in preterm birth rates between the two groups. The investigators concluded that treating periodontal disease during pregnancy did not affect the risk of preterm birth. However, they also found that there were more stillbirths in the group that received treatment after pregnancy, suggesting that periodontal treatment may improve survival of fetuses. The potential bias resulting from the intervention affecting both the outcome (in this case, preterm birth) and survival (in this case, stillbirth) was acknowledged as a limitation.