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Table 1 Rates of respiratory distress syndrome (RDS) per 1000 fetuses at risk at early (<32 weeks) and late (≥39 weeks) gestation and unadjusted odds ratios and 95 % confidence intervals (CI) expressing the association between maternal and infant characteristics and RDS, United States, 2005–2006

From: Heterogeneity of respiratory distress syndrome: risk factors and morbidity associated with early and late gestation disease

Risk factors RDS <32 weeks RDS ≥39 weeks
Cases Fetuses at risk Rate/1000a Odds ratiosb [95 % CI] Casess Fetuses at risk Rate/1000a Odds ratiosb [95 % CI]
Age <20 years 959 434,604 2.2 1.38 [1.29, 1.48] 545 272,042 2.0 1.25 [1.14, 1.37]
20–34 5314 3,312,305 1.6 Reference 3249 2,024,271 1.6 Reference
≥35 1177 621,356 1.9 1.06 [1.04, 1.08] 493 354,606 1.4 0.95 [0.92, 0.98]
Multi-fetal gestation 2169 150,761 14.4 11.6 [11.1, 12.2] 41 7103 5.8 3.61 [2.65, 4.91]
Smoking 1081 450,149 2.4 1.48 [1.39, 1.58] 582 253,288 2.3 1.49 [1.36, 1.62]
Diabetes 445 163,802 2.7 1.63 [1.48, 1.80] 207 74,377 2.8 1.76 [1.53, 2.02]
Chronic hypertension 355 47,353 7.5 4.60 [4.13, 5.12] 49 17,144 2.9 1.78 [1.34, 2.36]
Congenital anomaly 1000 64,417 15.5 10.5 [9.83, 11.2] 358 31,777 11.3 7.59 [6.81, 8.46]
Male sex 4004 2,235,753 1.8 1.11 [1.06, 1.16] 2581 1,340,148 1.9 1.48 [1.39, 1.57]
All 7450 4,368,265 1.7 - 4287 2,650,919 1.6 -
  1. aRates of RDS <32 weeks represent cumulative incidence from 24 to 31 weeks (8 week period) and cannot be directly compared with rates of RDS ≥39 weeks which represent cumulative incidence from 39 to 43 weeks (5 week period)
  2. bOdds ratios were estimated by contrasting the RDS rate among those with and those without the risk factor e.g., RDS < 32 weeks among infants of smokers vs nonsmokers. Since odds ratios express the relative effect of risk factors on RDS, the odds ratios for early gestation RDS can be directly compared with the odds ratios for late gestation RDS