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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