Table 5.

Odds ratios (ORs) of socioeconomic status (SES) for SGA after adjustments for maternal and pregnancy characteristics and other significant risk factors for SGA

	Model 1	Model 2	Model 3		Model A		Model B		Model C		Model D
SES	OR (95% CI)	OR (95% CI)	OR (95% CI)	Diff. with 2 (%)*	OR (95% CI)	Diff. with 3 (%)*	OR (95% CI)	Diff. with 3 (%)*	OR (95% CI)	Diff. with 3 (%)*	OR (95% CI)	Diff. with 3 (%)*
Upper white-collar	1	1	1		1		1		1		1
Lower white-collar	1.16 (1.11 − 1.21)	1.24 (1.18 − 1.29)	1.14 (1.09 − 1.20)	41.7	1.14 (1.09 − 1.19)	-	1.14 (1.09 − 1.20)	-	1.14 (1.09 − 1.19)	-	1.14 (1.09 − 1.19)	-
Blue-collar	1.42 (1.35 − 1.48)	1.57 (1.49 − 1.64)	1.28(1.21 − 1.34)	50.9	1.28 (1.22 − 1.35)	-	1.27 (1.21 − 1.34)	3.6	1.27 (1.21 − 1.34)	3.6	1.27 (1.21 − 1.33)	3.6
Other	1.19 (1.14 − 1.25)	1.28 (1.22 − 1.34)	1.19 (1.14 − 1.25)	32.1	1.18 (1.13 − 1.24)	5.3	1.18 (1.13 − 1.24)	5.3	1.19 (1.13 − 1.25)	-	1.18 (1.12 − 1.24)	5.3
Missing	1.36 (1.19 − 1.30)	1.39 (1.32 − 1.46)	1.24 (1.18 − 1.31)	38.5	1.25 (1.19 − 1.32)	-	1.23 (1.17 − 1.29)	4.2	1.24 (1.18 − 1.30)	-	1.22 (1.16 − 1.29)	8.3

*(The contribution of each factor was calculated as the percentage reduction in the OR of SES compared to Model 3 using the formula (OR Model 3 – OR Model A/B/C/D) / (OR Model 3 – 1).

Model 1 = Adjusted by SES.

Model 2 = Adjusted by SES + age and parity.

Model 3 = Adjusted by Model 2 + smoking.

Model A = Adjusted by Model 3 + place of residence grouped by hospital district.

Model B = Adjusted by Model 3 + major congenital anomaly.

Model C = Adjusted by Model 3 + amniocentesis.

Model D = Adjusted by Model 3 + amniocentesis + placenta previa + placental abruption + major congenital anomaly + prior cesarean section.