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Table 2 Association between maternal and offspring preterm birth, Manitoba, Canada, 1980–2016

From: Revisiting the association between maternal and offspring preterm birth using a sibling design

Maternal gestational age

Infant’s preterm birth cases/No of births

Preterm birth rate, %

URR

95% CI

ARR c

95% CI

Population cohorta (N = 79,198)

 Not Preterm

4588/75,427

6.08

1.00

Reference

1.00

Reference

 Preterm (24–36 weeks)

325/3771

8.62

1.42

1.27, 1.58

1.39

1.25, 1.54

 Very Preterm (24–31 weeks)

35/326

10.74

1.77

1.28, 2.42

1.76

1.29, 2.41

 Moderately Preterm (32–36 weeks)

290/3445

8.43

1.38

1.24, 1.55

1.35

1.21, 1.51

Sibling subcohortb (N = 2499)

 Not Preterm

143/1430

10.00

1.00

Reference

1.00

Reference

 Preterm (24–36 weeks)

109/1069

10.20

1.02

0.77, 1.36

1.02

0.77, 1.34

 Very Preterm (24–31 weeks)

7/80

8.75

0.88

0.39, 1.96

0.88

0.38, 2.02

 Moderately Preterm (32–36 weeks)

102/989

10.31

1.03

0.77, 1.38

1.03

0.78, 1.36

  1. Abbreviations: URR Unadjusted Relative Risk, ARR Adjusted Relative Risk, CI confidence intervals
  2. aAnalyzed with a log-binomial regression model
  3. bAnalyzed with a GEE fixed-effects log-binomial regression model
  4. cAdjusted for whether mother moved or had a substance abuse diagnosis in year before birth of child, child’s birth year, mother’s age at birth of child, neighborhood location and SES at birth of child, child’s sex and child’s birth order