Table.

Relative risk (per unit increase in variable) of Down’s syndrome for age, parity, gravidity, and previous miscarriage, 1986-95 and 1986-90, South Australia

Variable	Births and terminations						Births only
	1986-95 (284 cases of Down’s syndrome, 197 912 births)			1986-90 (128 cases of Down’s syndrome, 98 561 births)			1986-95 (171 cases of Down’s syndrome, 197 912 births)			1986-90 (100 cases of Down’s syndrome, 98 561 births)
	Relative risk (95% CI)	P value		Relative risk (95% CI)	P value		Relative risk (95% CI)	P value		Relative risk (95% CI)	P value
Univariate analysis
Age	1.202 (1.142 to 1.266)	0.0001		1.170 (1.097 to 1.247)	0.0001		1.129 (1.103 to 1.155)	0.0001		1.131 (1.099 to 1.165)	0.0001
Parity	1.256 (0.997 to 1.581)	0.0769		1.260 (0.946 to 1.677)	0.1461		1.235 (1.105 to 1.380)	0.0006		1.245 (1.078 to 1.438)	0.0059
Gravidity	1.176 (0.988 to 1.398)	0.0931		1.168 (0.940 to 1.452)	0.1944		1.131 (1.036 to 1.235)	0.0099		1.107 (0.977 to 1.254)	0.1269
Previous miscarriage	1.148 (0.769 to 1.715)	0.5307		1.066 (0.599 to 1.896)	0.8338		1.078 (0.849 to 1.370)	0.5526		0.883 (0.559 to 1.394)	0.5751
Multivariate analysis
Parity and age:
Parity	0.964 (0.777 to 1.196)	0.7378		0.990 (0.751 to 1.306)	0.9442		1.038 (0.942 to 1.145)	0.4554		1.032 (0.912 to 1.168)	0.6215
Age	1.206 (1.142 to 1.273)	0.0001		1.171 (1.093 to 1.254)	0.0001		1.125 (1.098 to 1.153)	0.0001		1.128 (1.094 to 1.163)	0.0001
Gravidity and age:
Gravidity	0.961 (0.810 to 1.141)	0.6463		0.972 (0.778 to 1.215)	0.8006		0.987 (0.909 to 1.071)	0.7541		0.949 (0.846 to 1.065)	0.3637
Age	1.208 (1.143 to 1.276)	0.0001		1.173 (1.095 to 1.258)	0.0001		1.130 (1.102 to 1.159)	0.0001		1.138 (1.100 to 1.177)	0.0001
Previous miscarriage and age:
Previous miscarriage	0.929 (0.642 to 1.344)	0.6865		0.875 (0.516 to 1.483)	0.6003		0.933 (0.777 to 1.121)	0.4480		0.743 (0.529 to 1.044)	0.0584
Age	1.205 (1.142 to 1.270)	0.0001		1.173 (1.098 to 1.254)	0.0001		1.131 (1.103 to 1.159)	0.0001		1.138 (1.098 to 1.179)	0.0001