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Timing and patterns of exposures during pregnancy and their implications for study methods
I Hertz-Picciotto1, L M Pastore, J J Beaumont
1Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, 27599, USA.
American Journal of Epidemiology
|March 15, 1996
Summary
Exposure variability during pregnancy can lead to misclassification bias in studies. Researchers introduced a new measure, the overall to time-window (OTW) ratio, to quantify this risk for accurate pregnancy outcome research.
Area of Science:
- Environmental Health
- Epidemiology
- Reproductive Health
Background:
- Pregnancy studies often use 'anytime-during-pregnancy' exposure data, which may not reflect critical exposure windows.
- Variability in exposure timing can introduce misclassification bias, affecting the accuracy of risk assessments for adverse pregnancy outcomes.
Purpose of the Study:
- To examine exposure variability across pregnancy for various factors in a rural California population.
- To introduce and evaluate a novel metric, the overall to time-window (OTW) ratio, for quantifying exposure variability and its impact on misclassification bias.
Main Methods:
- A population-based sample of 357 livebirths from 10 rural California counties was analyzed.
- Exposure data for medical, lifestyle, residential, and occupational factors were collected.
- The overall to time-window (OTW) ratio was calculated to assess exposure variability and potential for misclassification.
Main Results:
- Exposures like smoking and residential factors showed low OTW ratios (1.1-1.3), indicating longer duration.
- Other exposures, including paint applications, influenza, and ultrasound, had higher OTW ratios (4-6), suggesting shorter, critical windows.
- Intertrimester concordance varied, with high agreement for smoking and low agreement for short-duration illnesses.
Conclusions:
- The anytime-during-pregnancy exposure index can bias associations between risk factors and adverse pregnancy outcomes, especially with high OTW ratios.
- Misclassification bias is a significant concern when exposure timing is not precisely captured, particularly in case-control studies.
- Detailed collection of exposure timing is crucial for accurate investigations of pregnancy outcomes, especially for variable exposures.