Interpregnancy intervals in the United States: data from the birth certificate and the national survey of family growth.

To describe data on interpregnancy intervals (IPI), defined as the timing between a live birth and conception of a subsequent live birth, from a subset of jurisdictions that adopted the 2003 revised birth certificate. Because this information is available among revised jurisdictions only, the national representativeness of IPI and related patterns to the entire United States were assessed using the 2006-2010 National Survey of Family Growth (NSFG).