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Table 1 λS and sib-sib OR (with 95% CI) for preterm birth.

From: Population-based estimate of sibling risk for preterm birth, preterm premature rupture of membranes, placental abruption and pre-eclampsia

  All races White Black
Population: preterm birth 9759 6232 3354
Population: N 268103 220728 42899
Population risk 0.036 (0.035–0.037) 0.028 (0.027–0.029) 0.078 (0.075–0.081)
Siblings: sibpairs with both siblings affected 1020 514 489
Siblings: sibpairs with first sibling affected 6522 4181 2210
Sibling risk 0.156 (0.147–0.165) 0.123 (0.113–0.133) 0.221 (0.204–0.238)
λS 4.3 (4.0–4.6) 4.4 (4.0–4.7) 2.8 (2.6–3.1)
Sib-sib unadjusted OR (95% CI) 5.6 (5.2–6.0) 5.7 (5.2–6.3) 3.6 (3.2–4.0)
Sib-sib adjusted OR (95% CI)# 4.2 (3.9–4.5) 5.1 (4.6–5.7) 3.3 (2.9–3.7)
  1. #Adjusted for mother < 20 years old, mother < 12 education, Medicaid (index of low SES), no prenatal care, mother BMI < 20 kg/m2, cigarette smoking