Table 4.

Delivery time and birth defects during 2003 - 2012 in Xi’an city

Year	Premature delivery with birth defects		Postmature delivery with birth defects		Normal delivery with birth defects		Premature delivery andnormal delivery			Postmature delivery andnormal delivery
	n	Incidence (%)	n	Incidence (%)	n	Incidence (%)	χ2	P	Contingency coefficient	χ2	P	Contingency coefficient
2003	119	9.57	9	1.25	260	0.65	1062.62	<0.001	0.1579	3.12*	0.078	0.0099
2004	108	7.87	6	0.78	303	0.65	813.01	<0.001	0.1294	0.18	0.674	0.0019
2005	105	4.32	17	1.80	295	0.57	442.06	<0.001	0.0902	23.65	<0.001	0.0212
2006	127	6.83	14	1.44	320	0.57	916.39	<0.001	0.1251	12.29	<0.001	0.0147
2007	135	5.54	11	0.83	450	0.59	790.49	<0.001	0.0994	1.31	0.252	0.0041
2008	196	7.42	27	2.07	465	0.50	1783.73	<0.001	0.1356	60.61	<0.001	0.0254
2009	220	7.27	20	1.46	584	0.62	1586.33	<0.001	0.1265	15.41	<0.001	0.0127
2010	281	7.88	13	0.91	623	0.61	2138.73	<0.001	0.1410	2.02	0.155	0.0044
2011	314	7.97	18	1.56	578	0.53	2682.34	<0.001	0.1524	22.40	<0.001	0.0143
2012	342	6.86	16	1.93	565	0.45	2867.40	<0.001	0.1463	36.52*	<0.001	0.0177
Total	1947	7.08	151	1.40	4443	0.56	14649.84	<0.001	0.1323	131.69	<0.001	0.0128

*Corrected for expected number <5.