title: Reconstructing a Pregnancy Cohort to Examine Potential Selection Bias in Studies on Racial Disparities in Preterm Delivery.
abstract: Epidemiologic studies examining preconception risk factors on perinatal outcomes are typically restricted to livebirths. By including only non-terminated pregnancies, estimates for the underlying pregnancy cohort may be subject to selection bias. We examined if potential selection bias due to induced termination by maternal race may result in different estimates of the non-Hispanic black - non-Hispanic white risk ratio (RR) for preterm delivery (PTD) among a reconstructed pregnancy cohort ('pseudo-pregnancy cohort').
  
  
  
  Using New York City registries of 1.6 million livebirths, spontaneous terminations, and induced terminations among non-Hispanic black and non-Hispanic white women (2000-12), we multiply imputed PTD (<37 weeks) and early PTD (<32 weeks) outcomes for induced terminations based on maternal race, age, parity, marital status, nativity, and medical care payer to construct the pseudo-pregnancy cohort.
  
  
  
  Among non-Hispanic black and non-Hispanic white women, 55% and 19% of pregnancies ended in induced termination and 13% and 8% resulted in PTD, respectively. Although several factors were associated with both PTD and induced termination, PTD RRs in the birth (RR 1.64, 95% confidence interval (CI) 1.62, 1.66) and pseudo-pregnancy (RR 1.63, 95% CI 1.56, 1.71) cohorts were similar. However, early PTD RR was somewhat larger in the birth (RR 2.80, 95% CI 2.71, 2.89) than pseudo-pregnancy (RR 2.47, 95% CI 2.23, 2.73) cohort.
  
  
  
  Using birth certificate data - thereby excluding induced terminations - to estimate the PTD racial disparity did not produce biased estimates. Our data suggest observed PTD disparities likely are not artefacts of selection bias due to induced termination.
authors: Department of Obstetrics and Gynecology, Weill Cornell Medical College, New York, NY.
authors: Katherine J
authors: KJ
authors: Sapra
authors: School of Public Health and Health Systems, University of Waterloo, Waterloo, ON, Canada.
authors: Ashok K
authors: AK
authors: Chaurasia
authors: Department of Obstetrics and Gynaecology, University of British Columbia, Vancouver, BC, Canada.
authors: Jennifer A
authors: JA
authors: Hutcheon
authors: Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Rockville, MD.
authors: Katherine A
authors: KA
authors: Ahrens
mesh_terms: D000028:Abortion, Induced / Q000706:statistics & numerical data; D000328:Adult; D015331:Cohort Studies; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D054625:Healthcare Disparities / Q000706:statistics & numerical data*; D006801:Humans; D007231:Infant, Newborn; D007348:Insurance, Health / Q000706:statistics & numerical data; D000068101:Maternal-Child Health Services / Q000706:statistics & numerical data*; D009519:New York City / Q000453:epidemiology; D010298:Parity; D011159:Population Surveillance; D011247:Pregnancy; D011256:Pregnancy Outcome; D037841:Pregnant People / Q000208:ethnology*; D047928:Premature Birth / Q000453:epidemiology* / Q000208:ethnology; D015983:Selection Bias; D055815:Young Adult
keywords: collider bias; induced termination; loss to follow-up; preterm birth; racial disparities; selection bias