1.2. Determination of stillbirth risk among relatives
We used logistic regression models to estimate the odds ratio (95% confidence interval [95%: CI]) of stillbirth, comparing the odds of stillbirth in relatives of parents of stillbirth cases to the odds of stillbirth in relatives of parents of live birth controls. Estimates were adjusted for birth year, race (whether non-Hispanic White), and ethnicity (whether Hispanic). Case-control statuses of FDRs, SDRs and TDRs of affected and unaffected parents were similarly ascertained using identical case and control definitions in probands. To identify distinct parent-of-origin effects on stillbirth, we conducted parental sex-specific analyses. Statistical analyses were carried out using SAS (version 9.4, SAS Institute Inc., Cary, NC), R (version 4.0.2), and STATA version 15.0 (StataCorp, College Station, TX).