1. Pregnancy-associated Crashes and Birth Outcomes: Linking birth/fetal death records to motor vehicle crash data Lisa Hyde, Larry Cook Lenora Olson, Hank Weiss, J. Michael Dean

2. Prior Fetal Injury Research l Research on the effects of motor vehicle crashes on fetal outcomes is limited – Lack of pregnancy information on crash records – Lack of motor vehicle crash history on birth certificates

3. Study Objective l Assess the effect of involvement in a motor vehicle crash on the likelihood of adverse events for the fetus l Use probabilistic linkage to combine motor vehicle crash and birth/fetal death records

4. Probabilistic Linkage Basics

5. Probabilistic Linkage Theory Crash Record Ambulance Record Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Probabilistic record linkage is a method of using statistical properties of variables common to a pair of records to calculate the probability that the records apply to the same person and event...

6. Probabilistic Linkage Theory Briefly, two statistical properties of each common variable -- reliability and discriminating power -- determine the odds ratio for a true match. The odds ratio is the uniformly most powerful test statistic for discriminating between matched and unmatched record pairs.

7. Probabilistic Linkage Theory Probability that a common variable agrees on a matched pair. Approximately 1 - error rate. Probability that a common variable agrees on an unmatched pair. Approximately 1 / number of values. Reliability (m) Discriminating Power (u)

8. Record Linkage with Imperfect Data Let us choose a pair of imperfect records and try to decide if they are a match. That is, do they refer to the same individual and event? Crash Records Crash Records Health Records Health Records

9. Probabilistic Record Linkage If each ambulance record matches to one crash record in a file of 100,000 crashes then the odds for a match at random are 1:99,999 Crash Records Crash Records Ambulance Records Ambulance Records

10. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Crash Record Ambulance Record First name agrees... m = 0.90 u = 0.01 ratio = 90:1 Agreement on first name improves the odds for a match: 1:99,999 x 90:1 = 1:1,111

11. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Crash Record Ambulance Record Last or middle name agrees with last or middle... m = 0.90 u = 0.04 ratio = 22:1 Agreement on last name improves the odds for a match: 1:1,111 x 22:1 = 1:51

12. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Sex agrees... m = 0.99 u = 0.50 ratio = 2:1 Crash Record Ambulance Record Agreement on sex improves the odds for a match: 1:51 x 2:1 = 1:25

13. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Crash Record Ambulance Record Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Date of Birth Month agrees... m = 0.99 u = 0.08 ratio = 12:1 Day agrees... m = 0.99 u = 0.03 ratio = 30:1 Year disagrees m = 0.99 u = 0.01 ratio = 1:99 Agreement on birth date improves the odds for a match: 1:25 x 4:1 = 1:6

14. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Crash Record Ambulance Record Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Date of Crash Month agrees... m = 0.99 u = 0.08 ratio = 12:1 Day agrees... m = 0.99 u = 0.03 ratio = 30:1 Year agrees m = 1.00 u = 1.00 ratio = 1:1 Agreement on crash date improves the odds for a match: 1:6 x 360:1 = 60:1

15. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Crash Record Ambulance Record Agreement on crash time improves the odds for a match: 60:1 x 12:1 = 1,699:1 Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Time of Crash Hour agrees... m = 0.90 u = 0.04 ratio = 23:1 Minute disagrees... m = 0.50 u = 0.02 ratio = 1:2

16. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Crash Record Ambulance Record Agreement on crash location improves the odds for a match: 1,699:1 x 10:1 = 16,990:1 Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Place of crash agrees... m = 0.99 u = 0.10 ratio = 10:1

17. Probabilistic Record Linkage Mary Smith F 05/05/45 07/15/96 11:47 Albany US5 Seat=1 Belt=N Mary Smith Sanchez F 05/05/44 07/15/96 11:55 Albany Fracture Mem Hosp Crash Record Ambulance Record This pair of records has both agreements and disagreements. Our calculations say that the odds are 16,990:1 that the records refer to the same individual and crash event.

18. Linkage of Motor Vehicle Crash Records with Birth and Fetal Death Certificates

19. Study Databases (1992-1999) l Utah Motor Vehicle Crash Data – All reported motor vehicle crashes – Collected by police officers at the crash scene – Only drivers l Utah Birth Certificate Data – All single live births in Utah l Utah Fetal Death Certificate Data – All reported fetal deaths after 20 weeks gestation – Excludes elective abortions

20. Linkage Variables l Mother’s first and last name l Mother’s date of birth l Date of infant birth or fetal death l Date of crash – Compared gestational age / date of last menses with date of crash to ensure the crash occurred during pregnancy

21. Statistical Analysis l Descriptive statistics and logistic regression were used to assess the impact of having an MVC during pregnancy and wearing a seatbelt on adverse outcomes l Adverse outcomes included: – Low birth weight (<2500 grams) – Excessive maternal bleeding – Fetal distress – Placental abruption

22. Covariates in Logistic Model l Age of the mother l Race l Weight gain l Education level l Smoking l Alcohol l Month of first prenatal visit l Number of previous births l Medical risk factors l Seatbelt use l Crash severity (KABCO) l Trimester of crash Birth certificate Crash database

23. Birth Certificate Results Crash Records to Birth Certificates (1992-1999)

24. Number of Motor Vehicle Crashes During Pregnancy n = 322,704 8,938 births with a crash (2.8%) 322,704 single live births in Utah, 1992 – 1997 8,938 (< 3%) were involved in an MVC during pregnancy

25. Crash n = 8,938 No Crash n = 313,766 Age25.6 years26.3 years* Smoking11.5%9.3%* Alcohol1.7%1.5% Number of Previous Births 1.21.3* Completed High School 85.9%85.6% Received Care 1st Trimester 84.6%83.5%* * Significant at 0.05 level

26. Trimester of Crash n = 8,938

27. Logistic Regression Results for Crash vs. No Crash Odds Ratio95% CI Low birth weight1.0(0.9, 1.1) Excessive bleeding1.0(0.7, 1.3) Fetal distress1.1(1.0, 1.2) Placental abruption1.0(0.8, 1.2) n = 322,704

28. Seatbelt n = 7,143 No Seatbelt n = 1,099 Age25.8 years23.9 years* Smoking9.8%21.2%* Alcohol1.6%2.6%* Number of Previous Births 1.21.3 Completed High School 88.1%73.2%* Received Care 1st Trimester 85.5%78.2%* * Significant at 0.05 level

29. Logistic Regression Results for No Seatbelt vs. No Crash Odds Ratio95% CI Low birth weight1.3(1.0, 1.6)* Excessive bleeding1.6(0.9, 2.9) Fetal distress1.0(0.8, 1.4) Placental abruption1.0(0.6, 1.8) * Significant at 0.05 level n = 322,704

30. Logistic Regression Results for No Seatbelt vs. Seatbelt EffectOdds Ratio95% CI Low birth weight1.2(0.9, 1.6) Excessive bleeding2.1(1.0, 4.2)* Fetal distress1.1(0.8, 1.5) Placental abruption0.9(0.4, 1.8) * Significant at 0.05 level n = 8,938

31. Fetal Death Certificate Results Crash Records to Fetal Death Certificates (1992-1999)

32. Fetal Death Results l 2,645 fetal deaths recorded during study period l 45 (1.7%) linked to a motor vehicle crash record 45 fetal deaths involved in a crash (1.7%) n = 2,645

33. Pregnancies Resulting in Fetal Death Belted crash Unbelted crash Unknown belt use Total pregnancies 7,1431,099696 Fetal deaths (Percent) 28 (0.4%) 12 (1.2%) 5 (0.7%) Unbelted pregnant women were 2.8 (95% CI 1.4, 5.6) times more likely to experience a fetal death than belted pregnant women

34. Conclusions l Probabilistic linkage is a feasible method to combine crash and birth records – Comparison group of women not in crashes – No recall bias / loss to follow-up l Failure to to wear a seatbelt may increase the likelihood of adverse fetal events

35. Questions? Larry Cook 615 Arapeen Dr., Suite 202 Salt Lake City, UT 84108 801.585.9760 larry.cook@hsc.utah.edu