Use of Meta-analyses by IARC Working Groups

van den Hooven et al. (2012) found a non­ significant association between high levels of maternal and fetal C­reactive protein (CRP) and exposure to air pollution when they examined the correlation of CRP levels with inflammation and obstetric morbidity. The authors reported that elevated fetal CRP levels at delivery were associated with higher long­term average maternal exposure to PM10 (particul ate matter ≤ 10 μm in aero dynamic diameter) and NO2 (nitrogen dioxide). Other studies have reported that neither pre eclampsia (Kristensen et al. 2009) nor pregnancy loss (Boggess et al. 2005) is associated with a systemic inflammation as reflected by CRP levels. However, van den Hooven et al. (2012) insisted that exposure to air pollution may lead to systemic inflammation in pregnancy. Although this statement is defensible, the confounding results regarding CRP levels should be clarified. CRP is accepted as a good marker of acute inflammation, particularly within infection, but its value in chronic inflamma­ tion depends on the inflammation pathway involved and the under lying process. In an examination of auto immune inflammatory responses triggered by the indoor environ­ ment in sick buildings, CRP was < 0.1 mg/dL (normal range, 0.1–0.5 mg/dL) in 27% of patients (Blasco 2011). Interestingly, 13% of patients had suffered miscarriages. CRP may be low or typically very low during a flare­up of some connective tissue dis orders, such as systemic lupus erythematosus (SLE) or undifferen tiated connective tissue disease. The erythro cyte sedimentation rate more accu­ rately reflects SLE disease activity in patients without associated infection. Therefore, the presence of normal or low CRP levels does not guarantee the absence of inflammation or a positive pregnancy outcome. It would be interesting to assess possible individual immune susceptibility markers and other markers, such as auto antibodies or tumor necrosis factor α, in future studies of sys­ temic inflammation induced by air pollutants during pregnancy. The author declares he has no actual or potential competing financial interests.