title: Outcomes of deliveries by family physicians or obstetricians: a population-based cohort study using an instrumental variable.
abstract: BACKGROUND
  Previous research has suggested that obstetric outcomes are similar for deliveries by family physicians and obstetricians, but many of these studies were small, and none of them adjusted for unmeasured selection bias. We compared obstetric outcomes between these provider types using an econometric method designed to adjust for unobserved confounding.
  
  
  METHODS
  We performed a retrospective population-based cohort study of all Canadian (except Quebec) hospital births with delivery by family physicians and obstetricians at more than 20 weeks gestational age, with birth weight greater than 500 g, between Apr. 1, 2006, and Mar. 31, 2009. The primary outcomes were the relative risks of in-hospital perinatal death and a composite of maternal mortality and major morbidity assessed with multivariable logistic regression and instrumental variable-adjusted multivariable regression.
  
  
  RESULTS
  After exclusions, there were 3600 perinatal deaths and 14,394 cases of maternal morbidity among 799,823 infants and 793,053 mothers at 390 hospitals. For deliveries by family physicians v. obstetricians, the relative risk of perinatal mortality was 0.98 (95% confidence interval [CI] 0.85-1.14) and of maternal morbidity was 0.81 (95% CI 0.70-0.94) according to logistic regression. The respective relative risks were 0.97 (95% CI 0.58-1.64) and 1.13 (95% CI 0.65-1.95) according to instrumental variable methods.
  
  
  CONCLUSIONS
  After adjusting for both observed and unobserved confounders, we found a similar risk of perinatal mortality and adverse maternal outcome for obstetric deliveries by family physicians and obstetricians. Whether there are differences between these groups for other outcomes remains to be seen.
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL. kaubrey@mun.ca.
authors: Kris
authors: K
authors: Aubrey-Bassler
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Richard M
authors: RM
authors: Cullen
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Alvin
authors: A
authors: Simms
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Shabnam
authors: S
authors: Asghari
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Joan
authors: J
authors: Crane
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Peizhong Peter
authors: PP
authors: Wang
authors: Primary Healthcare Research Unit, Discipline of Family Medicine (Aubrey-Bassler, Cullen, Asghari, Godwin), Department of Geography (Simms), Discipline of Obstetrics and Gynecology (Crane) and Division of Community Health and Humanities (Wang), Memorial University of Newfoundland, St. John's, NL.
authors: Marshall
authors: M
authors: Godwin
mesh_terms: D002170:Canada; D015331:Cohort Studies; D036861:Delivery, Obstetric / Q000379:methods*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D008428:Maternal Mortality; D009774:Obstetrics / Q000379:methods*; D054238:Perinatal Mortality; D010821:Physicians, Family; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies; D018570:Risk Assessment; D013038:Specialization