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Table 5 HI-titer in relation to risk of pre-eclampsia, preterm birth, small for gestational age birth, and birth weight

From: Risk of pregnancy complications and adverse birth outcomes after maternal A(H1N1)pdm09 influenza: a Norwegian population-based cohort study

  HI-titer = 5, n = 575 HI-titer ≥10, n = 201
Pre-eclampsia
 Cases, n (%) 16 (2.8) 5 (2.5)
 Crude OR (95% CI) 1 (Ref) 0.89 (0.32, 2.46)
 Adjusted OR (95% CI)a 1 (Ref) 0.83 (0.29, 2.36)
Preterm birth
 Cases, n (%) 13 (2.3) 6 (3.0)
 Crude OR (95% CI) 1 (Ref) 1.33 (0.50, 3.55)
 Adjusted OR (95% CI)a 1 (Ref) 1.26 (0.47, 3.40)
Small for gestational age birth
 Cases, n (%) 45 (7.8) 20 (10.0)
 Crude OR (95% CI) 1 (Ref) 1.30 (0.75, 2.26)
 Adjusted OR (95% CI)a 1 (Ref) 1.30 (0.74, 2.81)
Birth weight
 10th percentile (g) 3000 2932
 Difference in 10th percentile, β (95% CI)b 1 (Ref) −123 (−248, 2)
 50th percentile (g) 3560 3580
 Difference in 50th percentile, β (95% CI)b 1 (Ref) −10 (− 97, 76)
  1. aLogistic regression adjusted for maternal age at birth (continuous), parity (primiparous/multiparous), smoking during pregnancy (yes/no), and time in days between birth and pandemic (continuous). The model was also adjusted for influenza risk group (yes/no) except with pre-eclampsia as the outcome
  2. bQuantile regression adjusted for maternal age at birth (continuous), parity (primiparous/multiparous), smoking during pregnancy (yes/no), influenza risk group (yes/no), and time in days between birth and pandemic (continuous)