FIGURE 2.

Estimate of the percentage of singleton preterm births in which obstetrical intervention affected gestational age at delivery: 19 US states, 2006.

^aStates using the 2003 revision of the US standard birth certificate.

^bBirths lacking data on method of delivery, whether or not labor was induced, and whether or not a trial of labor was attempted are excluded.

^cInduction of labor (attempted or successful).

^dNo reported precipitous, prolonged, or augmented labor; fetal intolerance of labor; or use of forceps or vacuum.