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Table 5 Rates of respiratory distress syndrome (RDS) at 32–36 weeks and 37–38 weeks per 1000 fetuses at risk 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 32–36 weeks RDS 37–38 weeks
Cases Fetuses at risk Rate/1000a Odds ratiosb [95 % CI] Cases Fetuses at risk Rate/1000a Odds ratiosb [95 % CI]
Age <20 years 1165 426,327 2.7 1.00 [0.94, 1.06] 360 386,323 0.93 0.83 [0.74, 0.92]
20–34 8969 3,265,775 2.7 Reference 3364 2,978,793 1.13 Reference
≥35 1808 610,342 3.0 1.03 [1.01, 1.04] 568 545,748 1.04 0.97 [0.95, 1.00]
Multi-fetal gestation 2770 133,526 20.7 9.61 [9.21, 10.0] 214 55,869 3.83 3.63 [3.16, 4.17]
Smoking 1613 441,604 3.7 1.37 [1.30, 1.44] 632 392,595 1.61 1.55 [1.42, 1.69]
Diabetes mellitus 996 160,801 6.2 2.35 [2.20, 2.51] 414 136,882 3.02 2.95 [2.67, 3.27]
Chronic hypertension 423 44,759 9.5 3.52 [3.19, 3.88] 126 35,036 3.60 3.35 [2.81, 4.01]
Congenital anomaly 832 61,034 13.6 5.26 [4.90, 5.65] 346 50,707 6.82 6.71 [6.01, 7.50]
Male sex 7130 2,200,877 3.2 1.42 [1.37, 1.47] 2739 1,994,128 1.37 1.70 [1.59, 1.81]
All 11,942 4,302,444 2.8 - 4292 3,910,864 1.10 -
  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