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Distribution of preterm births (PTB) for singleton pregnancies in the United States for the year 2013a
| PTB Category | Gestation age (weeks) | Incidence in USA 2013 | Percentage of PTB |
|---|---|---|---|
| Extremely preterm | <28 | 0.58 | 5.9 |
| Severe or very preterm | 28–31 | 0.96 | 9.9 |
| Moderately preterm | 32–33 | 1.18 | 12.2 |
| Late preterm or near term | 34–36 | 6.99 | 72.0 |
aAdapted from United States National Vital Statistics Reports 2015 [132]
