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Table 3 Relative contribution of changes in the gestational age distribution and in gestational age-specific small-for-gestational age (SGA) rates to the overall temporal changes in sga rates among singleton live births in the United States (1990–1992 vs. 2002–2004; 2002–2004 vs. 2008–2010)

From: The association between temporal changes in the use of obstetrical intervention and small- for-gestational age live births

Period Gestational Age (weeks) Modified Kitagawa decomposition (per 10,000 fetuses-at-risk)
Contribution of changes in Total change Relative contribution of changes in
Gestational age Gestational age-specific SGA   Gestational age (%) Gestational age-specific SGA (%)
1990–1992 vs. 2002–2004 24–33 weeks 0.00 4.58 4.58 0.0 100.0
34–36 weeks −0.37 9.71 9.34 −4.0 104.0
37–38 weeks −8.83 55.44 46.61 −18.9 118.9
39–40 weeks −168.20 33.63 −134.57 125.0 −25.0
41 weeks −34.71 1.98 −32.73 106.0 −6.0
≥42 weeks −16.53 −0.48 −17.01 97.2 2.8
Total −228.65 104.87 −123.78 184.7 −84.7
2002–2004 vs. 2008-2010 24–33 weeks 0.01 −0.31 −0.30 −3.3 103.3
34–36 weeks 0.12 −0.26 −0.14 −85.7 185.7
37–38 weeks 0.48 24.75 25.23 1.9 98.1
39–40 weeks −38.16 45.14 6.99 −546.2 646.2
41 weeks −9.58 0.95 −8.63 111.0 −11.0
≥42 weeks −1.84 0.09 −1.74 105.3 −5.3
Total −48.96 70.36 21.41 −228.7 328.6