Risk of preeclampsia from exposure to particulate matter (PM₂.₅) speciation chemicals during pregnancy.

Objective: To determine whether maternal exposure to particulate matter (PM₂.₅) speciation chemicals during pregnancy is associated with the risk of preeclampsia.

Methods: We allocated average daily exposure values for 36 ambient particulate matter speciation chemicals to mothers during their first trimester and their entire pregnancy.

Twins born over weekends: are they at risk for elevated infant mortality?

Objective: To assess the impact of the day of birth on twin mortality in a population sample.

Methods: We analyzed weekend versus weekday twin births from the United States national twin birth data for the periods 1989-2002. We computed adjusted hazard ratios (HR) and 95% confidence intervals (CI) to assess the association between infant mortality and weekday of birth using the Cox proportional hazards model.