Factors associated with birthweight decline in Japan (1980–2004)

Table 1 Correlation of variables with birthweight (1980–2004) and change in variables between 1980 and 2004

variables	units	correlation with birthweight		1980 (n = 1,569,777)		2004 (n = 1,110,721)
variables	units	r²	p-value	mean	SD	mean	SD
Birthweight	grams			3190	444	3014	441
Gestational age	weeks	0.2787	< 0.0001	39.25	1.66	38.86	2.10
Father age	years of age	0.0007	< 0.0001	30.33	4.21	31.68	5.62
Mother age	years of age	0.0003	< 0.0001	27.62	3.75	29.69	4.72
Delivery number	including present birth	0.0084	< 0.0001	1.80	0.84	1.70	0.82
Multiple gestation	1 = singleton 2 = multiple birth	0.05	< 0.0001	1.02	0.13	1.02	0.15
live birth number	including present birth	0.0078	< 0.0001	1.78	0.83	1.69	0.81
Neonatal gender	1 = male 2 = female	0.0086	< 0.0001	1.49	0.50	1.49	0.50
Year	A.D.	0.0183	< 0.0001
Prefecture number	1 to 47	0.0004	< 0.0001

ISSN: 1471-2393