Table 1.

Rates of preterm births by period before and after exclusions

Periods	1991-1995	1996-2000	2001-2008
Rates	%	%	%
Preterm births before excluded values	4.70	4.90	5.90
(n)	(1 354 711)	(1 258 750)	(1 861 983)
Preterm births after excludes values	4.42	4.71	5.65
(n)	(1 323 021)	(1 232 824)	(1 836 582)

Chile, Singletons Live Births, 1991-2008.