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Table 3 Frequencies and adjusted odds ratios for preterm birth by antenatal model of care and psychosocial risk characteristics, British Columbia, April 1, 2008-December 31, 2012

From: Improving birth outcomes for women who are substance using or have mental illness: a Canadian cohort study comparing antenatal midwifery and physician models of care for women of low socioeconomic position

Preterm birth by model of care
  MW n = 3394 GP n = 25,753 OB n = 4746 MW vs. GP MW vs. OB GP vs. OB
n(%) n(%) n(%) aOR (95% CI) aOR (95% CI) aOR (95% CI)
Mental illnessa
 Yes 56/1011 (5.54) 344/4917 (7.00) 71/545 (13.03) 0.92 (0.68–1.24) 0.49 (0.34–0.72) *0.54 (0.41–0.71)
 No 98/2383 (4.11) 1257/20,836 (6.03) 352/4201 (8.38) 0.73 (0.59–0.91) 0.51 (0.41–0.65) 0.70 (0.61–0.79)
Substance useb
 Yes 8/152 (5.26) 215/2276 (9.45) 39/182 (21.43) 0.59 (0.29–1.21) *0.24 (0.11–0.54) *0.41 (0.28–0.61)
 No 146/3242 (4.50) 1386/23,477 (5.90) 384/4564 (8.41) 0.80 (0.67–0.96) 0.55 (0.45–0.68) 0.69 (0.61–0.79)
Teen mother
 Yes (14–19 yrs.) 9/117 (7.69) 187/2584 (7.24) 21/206 (10.19) 1.09 (0.55–2.19) 0.74 (0.33–1.66) 0.67 (0.42–1.09)
 No (25–29 yrs.) 46/1161 (3.96) 475/7705 (6.16) 100/1371 (7.29) 0.69 (0.50–0.94) 0.56 (0.39–0.80) 0.81 (0.65–1.02)
Social assistancec
 Yes 17/239 (7.11) 299/3617 (8.27) 61/534 (11.42) 0.89 (0.53–1.50) 0.63 (0.36–1.12) 0.71 (0.53–0.96)
 No 137/3155 (4.34) 1302/22,136 (5.88) 362/4212 (8.59) 0.78 (0.64–0.94) 0.51 (0.42–0.63) 0.66 (0.58–0.75)
Neigh. SEPd
 Low/Medium 135/2944 (4.59) 1429/22,915 (6.24) 397/4369 (9.09) 0.80 (0.66–0.96) 0.52 (0.42–0.64) 0.65 (0.58–0.74)
 High 19/450 (4.22) 172/2838 (6.06) 26/377 (6.90) 0.72 (0.44–1.17) 0.63 (0.34–1.17) 0.88 (0.57–1.36)
Mental illness, substance use
 Both 5 or less /95e 95/927 (10.25) 18/76 (23.68) 0.43 (0.15–1.19) *0.18 (0.06–0.55) *0.41 (0.23–0.74)
 Neither 94/2325 (4.04) 1134/19,438 (5.83) 331/4090 (8.09) 0.73 (0.59–0.91) 0.52 (0.41–0.66) 0.71 (0.62–0.81)
Mental illness, social assistance
 Both 7/128 (5.47) 117/1195 (9.79) 27/161 (16.77) 0.58 (0.26–1.32) 0.35 (0.14–0.86) 0.60 (0.38–0.96)
 Neither 88/2272 (3.87) 1075/18,414 (5.84) 318/3828 (8.31) 0.70 (0.56–0.88) 0.48 (0.37–0.61) 0.68 (0.59–0.79)
Substance use, social assistance
 Both 5 or less /45e 94/832 (11.30) 22/93 (23.66) 0.78 (0.27–2.27) 0.34 (0.11–1.10) 0.44 (0.26–0.76)
 Neither 133/3047 (4.36) 1178/20,643 (5.71) 345/4118 (8.38) 0.78 (0.65–0.95) 0.53 (0.43–0.65) 0.67 (0.59–0.77)
  1. Abbreviations: MW midwife, GP general practitioner, OB obstetrician, OR odds ratio, CI confidence interval
  2. aMental illness included any of the following diagnoses prior to, or during the current pregnancy: anxiety disorder, depression, postpartum depression, bipolar disorder, other/unknown (including schizophrenic, mood, and psychotic disorders). Aside from mild anxiety or depression, a physician would diagnose mental illness
  3. bSubstance use included any indication in the medical record of heroin/opioids, cocaine, methadone, solvents, marijuana or other/unknown drugs used by the mother at any time during pregnancy, as well as prescription or other drug use identified as a risk by the provider
  4. cSocial assistance recipients received public financial assistance during the year of delivery due to low income
  5. dNeighbourhood low/medium socioeconomic position included women residing in the four lowest income quintiles, depending on residential postal code at delivery
  6. ePercentage suppressed due to small cell size
  7. *Outcomes had statistically significant tests of interaction (p < 0.10) comparing difference of effect across strata (yes vs. no)
  8. Models adjusted for all variables listed except stratifying variables: maternal age, medical risk, obstetric risk, pre-pregnancy BMI, infant sex, receipt of social assistance, smoking status, substance use, mental illness/disorder, neighbourhood SEP, Local Health Area socioeconomic rank, and northern residence
  9. Odds ratios based on 2178 PTB births and 33,893 total births with no missing information for this analysis