Table 1. Population characteristics.

	Extremely affected region						Moderately affected region						Slightly or unaffected region
	Male		Pa	Female		Pa	Male		Pa	Female		Pa	Male		Pa	Female		Pa
	2010	2011		2010	2011		2010	2011		2010	2011		2010	2011		2010	2011
Total	14 837	14 059		13 980	13 625		139 136	136 717		131 766	129 412		200 308	197 536		188 452	187 782
(%)	51.5	50.8		48.5	49.2		51.4	51.4		48.6	48.6		51.5	51.3		48.5	48.7
Singleton	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012		184 932	184 244
(%)	98.3	98.3		98.4	98.3		98.3	98.4		98.2	98.3		98.2	98.2		98.1	98.1
Mean gestational duration (day)	274.9	274.8	0.6	275.8	275.6	0.14	274.2	274.2	0.9	275.4	275.3	0.047	274.5	274.4	0.006	275.6	275.6	0.9
SD	10.8	10.7		10.8	10.8		10.8	10.8		10.5	10.5		10.8	10.9		10.6	10.5
(n)	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012
Preterm birth	705	625	0.2	524	513	0.9	6748	6664	0.8	4961	4961	0.7	9716	9814	0.09	7245	7003	0.07
(%)	4.8	4.5		3.8	3.8		4.9	5.0		3.8	3.8		4.9	5.1		3.9	3.8
(n)	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012		184 932	184 244
Mean birth weight (g)	3071.9	3077.2	0.3	2984.4	2986.5	0.7	3062.9	3067.0	0.01	2978.4	2978.2	0.9	3063.9	3067.1	0.02	2976.7	2982.1	<0.0001
SD	414.3	410.3		401.5	403.2		414.1	414.2		397.7	397.1		416.6	419.3		401.3	401.0
(n)	14 582	13 817		13 762.0	13 389		136 729	134 505		129 380	127 156		196 703	193 998		184 921	184 230
Low-birth-weight infants	977	874	0.2	1201	1183	0.8	9532	9214	0.2	11 653	11 331	0.4	13 922	13 716	0.9	17 165	16 629	0.007
(%)	6.7	6.3		8.7	8.8		7.0	6.9		9.0	8.9		7.1	7.1		9.3	9.0
(n)	14 582	13 817		13 762	13 389		136 729	134 505		129 380	127 156		196 703	193 998		184 921	184 230
Mean maternal age at birth	29.9	30.1	0.02	29.9	30.2	<0.0001	31.1	31.2	<0.0001	31.1	31.2	<0.0001	30.4	30.5	<0.0001	30.4	30.5	<0.0001
SD	5.0	5.1		5.1	5.1		5.0	5.0		5.0	5.0		5.0	5.0		5.0	5.1
(n)	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012		184 932	184 244
Mean birth order	1.78	1.80	0.07	1.77	1.81	0.0004	1.68	1.69	0.02	1.67	1.68	0.045	1.76	1.77	0.0002	1.76	1.78	<0.0001
SD	0.88	0.90		0.88	0.89		0.83	0.82		0.82	0.82		0.87	0.88		0.88	0.89
(n)	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012		184 932	184 244
First-born	6516	6111	0.4	6299	5823	0.0002	68 410	66 566	0.005	65 077	63 220	0.003	90 918	88 579	0.0004	85 014	83 345	<0.0001
(%)	44.7	44.2		45.8	43.5		50.0	49.5		50.3	49.7		46.2	45.7		46.0	45.2
(n)	14 583	13 817		13 763	13 389		136 735	134 515		129 389	127 162		196 722	194 012		184 932	184 244

SD, standard deviation.

^aP values were calculated by Chi-square test (categorical variables) and Student’s t-test (continuous variables).