Document Detail

Selection bias associated with contraceptive practice in time-to-pregnancy studies.
MedLine Citation:
PMID:  8154699     Owner:  NLM     Status:  MEDLINE    
In studies of subfertility using data on time to pregnancy (the number of noncontracepting menstrual cycles required to conceive), many pregnancies are not included in analyses because time-to-pregnancy data cannot always be collected. Birth control failures are one such group (couples who are using birth control regularly or sporadically, but become pregnant anyway). The more fecund couples are more likely to have birth control failures, and consequently, more likely to be excluded from analyses. If an exposure of interest is associated with irregular use of birth control or with the choice of less effective methods of birth control, the fecundability in the exposed (based on data from couples who can provide adequate time to pregnancy data) will be underestimated. Such bias may account for the findings in the literature showing reduced fecundability among smokers. More generally, when a subset of couples who differ in their fecundability are excluded from analysis, there will be opportunity for selection bias to produce under or overestimation of the strength of an association between an exposure and fecundability. This problem affects both retrospective and prospective studies. Time-to-pregnancy studies need to be designed to minimize this potential bias and to collect data to evaluate it adequately.
D D Baird; C R Weinberg; P Schwingl; A J Wilcox
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Publication Detail:
Type:  Journal Article; Review    
Journal Detail:
Title:  Annals of the New York Academy of Sciences     Volume:  709     ISSN:  0077-8923     ISO Abbreviation:  Ann. N. Y. Acad. Sci.     Publication Date:  1994 Feb 
Date Detail:
Created Date:  1994-05-06     Completed Date:  1994-05-06     Revised Date:  2005-11-16    
Medline Journal Info:
Nlm Unique ID:  7506858     Medline TA:  Ann N Y Acad Sci     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  156-64     Citation Subset:  IM    
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
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MeSH Terms
Contraception / statistics & numerical data*
Epidemiologic Methods
Menstrual Cycle
Pregnancy / statistics & numerical data*
Prospective Studies
Retrospective Studies
Selection Bias*
Time Factors

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