title: Cohort Variation in Selection During Pregnancy and Risk of Selected Birth Defects Among Males.
abstract: The literature theorizes, but does not test, that variation over time in selective loss in utero affects the observed count of live-born birth defects cases. We test the hypothesis that the risk of birth defects among live-born males varies inversely with the strength of selection against males in utero.
  
  
  
  We identified a subset of six birth defect phenotypes among males from the California Birth Defects Monitoring Program, an active surveillance system for over 490,000 male singletons born in eight California counties from 1986 to 2004. We assigned each birth defect case infant to a monthly conception cohort at risk of selection in utero. We used the monthly sex ratio at birth (M:F), derived from each conception cohort, as the indicator of selection against males. We analyzed the odds ratio of birth defects with both individual-level logistic regression and aggregate time-series methods.
  
  
  
  Consistent with selection in utero, male infants from conception cohorts with low outlying sex ratios (i.e., stronger selectivity) exhibit fewer than expected birth defects (adjusted odds ratio [OR] = 0.86; 95% confidence interval [CI] = 0.76, 0.98). Aggregate time-series tests also yield similar findings (OR = 0.81; 95% CI = 0.71, 0.90).
  
  
  
  Our findings among males indicate that variation in the strength of selectivity in utero accounts for a portion of observed cohort differences in morbidity due to birth defects. These findings suggest that "revealed prevalence" of morbidity across birth cohorts varies, at least in part, from selective loss in utero. See video abstract at, http://links.lww.com/EDE/B209.
authors.affiliation: From the aProgram in Public Health, University of California, Irvine, Irvine, CA; bSchool of Public Health, University of California, Berkeley, Berkeley, CA; and cDivision of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA.
authors.forename: Tim A
authors.initials: TA
authors.lastname: Bruckner
authors.forename: Deborah
authors.initials: D
authors.lastname: Karasek
authors.forename: Wei
authors.initials: W
authors.lastname: Yang
authors.forename: Gary M
authors.initials: GM
authors.lastname: Shaw
authors.forename: Ralph A
authors.initials: RA
authors.lastname: Catalano
mesh_terms: D000328:Adult; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D000013:Congenital Abnormalities / Q000453:epidemiology* / Q000235:genetics*; D005260:Female; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D050498:Live Birth; D016015:Logistic Models; D008297:Male; D015997:Neonatal Screening / Q000379:methods*; D016017:Odds Ratio; D011247:Pregnancy; D057216:Propensity Score; D012189:Retrospective Studies; D018570:Risk Assessment; D012737:Sex Factors