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Table 6 HI-titer in relation to risk of pre-eclampsia, preterm birth, small for gestational age birth, and birth weight in women with pregnancy start before October 1, 2009

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 = 293 HI-titer ≥10, n = 118
Pre-eclampsia
 Cases, n (%) 6 (2.0) 2 (1.7)
 Crude OR (95% CI) 1 (Ref) 0.82 (0.16, 4.15)
 Adjusted OR (95% CI)a 1 (Ref) 0.98 (0.18, 5.46)
Preterm birth
 Cases, n (%) 7 (2.4) 3 (2.5)
 Crude OR (95% CI) 1 (Ref) 1.07 (0.27, 4.19)
 Adjusted OR (95% CI)a 1 (Ref) 1.30 (0.31, 5.41)
Small for gestational age birth
 Cases, n (%) 17 (5.8) 11 (9.3)
 Crude OR (95% CI) 1 (Ref) 1.67 (0.76, 3.68)
 Adjusted OR (95% CI)a 1 (Ref) 1.75 (0.77, 3.97)
Birth weight
 10th percentile (g) 3070 2940
 Difference in 10th percentile, β (95% CI)b 1 (Ref) −159 (−309, −9)
 50th percentile (g) 3560 3610
 Difference in 50th percentile, β (95% CI)b 1 (Ref) −31 (− 158, 96)
  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)