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. Author manuscript; available in PMC: 2014 Jan 19.
Published in final edited form as: Lancet. 2012 Nov 16;381(9862):223–234. doi: 10.1016/S0140-6736(12)61856-X

Figure 5. Analysis of factors contributing to the increasing preterm birth rate in the United States (1989 to 2004).

Figure 5

Notes: See webappendix p.7-14 for details of analyses. Calculation of PAR aimed to take into account the existence of multiple risk factors in one woman, eg increased maternal age and ART use