Table 2:

Evaluation of overall confidence in body of evidence

Initial Confidence by Key Features of Study Design	Factors Increasing Confidence	Factors Decreasing Confidence	Confidence in the Body of the Evidence
Moderate Features: exposure occurs prior to outcome, individual outcome data, and comparison groups used	Risk of Bias – no studies were uninformative, half were considered low confidence, and half were medium to high (1) confidence (=)	Residual confounding – studies examining co-pollutant confounding did not observe an impact on observed associations. Not possible to evaluate if other residual confounding would bias toward or away from null without more information (=)	Moderate
	Publication bias expected to have minimal impact (=)	Concentration response - not evaluated (=)
	Indirectness – studies are of relevant populations and examine ambient exposures of interest (=)	Consistency – while there was substantial heterogeneity, associations are not so dissimilar to change interpretation, study design and population size did not contribute to heterogeneity (=)
	Imprecision – confidence intervals are generally of reasonable to narrow range, except in very small study populations (=)	Magnitude of effect – magnitudes are small, as would be expected in epidemiology studies of environmental exposures and birth outcomes (=)