Table 3. Factors of preterm labor/ectopic pregnancy stratified by the variables listed in the table by using Cox regression.

Events	Preterm labor								Ectopic pregnancy
PID	With PID		Without PID		With PID vs. Without PID (Reference)				With PID		Without PID		With PID vs. Without PID (Reference)
Stratified	Events	Rate	Events	Rate	Adjusted HR	95% CI	95% CI	P	Events	Rate	Events	Rate	Adjusted HR	95% CI	95% CI	P
Total	561	1,208.18	1,492	532.46	1.864	1.482	2.062	<0.001	14	30.15	33	11.78	2.121	1.803	3.776.	0.003
Age group (years)
12–19	12	3,215.26	43	2,777.33	0.969	0.878	1.069	0.264	0	0	2	129.18	0.000	-	-	0.842
20–29	295	2,801.93	725	1,527.55	1.535	1.391	1.694	<0.001	8	75.98	12	25.28	2.649	1.403	5.007	<0.001
30–39	240	1,543.12	683	788.92	1.637	1.484	1.806	<0.001	5	32.15	14	16.17	1.753	0.928	3.312	<0.001
40–49	14	111.54	41	66.20	1.410	1.278	1.556	<0.001	1	7.97	5	8.07	0.870	0.461	1.644	0.597
50–55	0	0	0	0	-	-	-	-	0	0	0	0	-	-	-	-
Insurance premium (NT$)
<18,000	543	1,200.98	1,458	534.11	1.882	1.705	2.076	<0.001	13	28.75	30	10.99	2.307	1.221	4.359	<0.001
18,000–34,999	15	1,478.78	27	479.19	2.583	2.341	2.849	<0.001	1	98.59	2	35.50	2.449	1.296	4.627	<0.001
≥35,000	3	1,453.28	7	438.85	2.772	2.512	3.058	<0.001	0	0	1	62.69	0.000	-	-	0.994
DM
Without	557	1,280.27	1,480	576.41	1.859	1.685	2.051	<0.001	14	32.18	33	12.85	2.207	1.169	4.171	<0.001
With	4	136.65	12	51.18	2.234	2.025	2.465	<0.001	0	-	0	-	-	-	-	-
HTN
Without	561	1,288.94	1,491	588.09	1.834	1.662	2.024	<0.001	13	29.87	33	13.02	2.023	1.071	3.823	<0.001
With	0	0	1	3.75	0.000	-	-	0.894	1	34.37	0	0.00	∞	-	-	0.987
Hyperlipidemia	561	1,227.64	1,492	543.45	1.899	1.721	2.095	<0.001	14	30.64	33	12.02	2.257	1.195	4.265	0.012
Obesity	561	1,209.77	1,492	533.14	1.899	1.721	2.095	<0.001	14	30.19	33	11.79	2.257	1.195	4.265	0.012
Heart disease	557	1,272.26	1,484	563.44	1.890	1.713	2.085	<0.001	14	31.98	32	12.15	2.320	1.229	4.385	<0.001
CKD	559	1,226.09	1,487	544.84	1.883	1.707	2.078	<0.001	14	30.71	32	11.72	2.309	1.222	4.363	<0.001
Season
Spring	128	1,279.80	368	572.93	1.869	1.694	2.062	<0.001	4	39.99	9	14.01	2.516	1.332	4.755	<0.001
Summer	153	1,275.16	379	525.13	2.032	1.842	2.242	<0.001	1	8.33	9	12.47	0.589	0.312	1.113	0.413
Autumn	163	1,167.24	375	472.75	2.066	1.873	2.280	<0.001	3	21.48	8	10.09	1.878	0.994	3.549	0.058
Winter	117	1,117.57	370	573.81	1.630	1.477	1.798	<0.001	6	57.31	7	10.86	4.654	2.464	8.795	<0.001
Urbanization level
1 (The highest)	178	1,242.98	489	554.34	1.877	1.701	2.070	<0.001	5	34.92	11	12.47	2.468	1.307	4.665	<0.001
2	269	1,286.41	684	559.40	1.925	1.744	2.123	<0.001	3	14.35	11	9.00	1.406	0.744	2.657	0.632
3	51	1,079.30	112	420.19	2.150	1.948	2.372	<0.001	1	21.16	4	15.01	1.243	0.658	2.349	0.481
4 (The lowest)	63	972.66	207	480.65	1.694	1.535	1.868	<0.001	5	77.20	7	16.25	4.187	2.217	7.912	<0.001
Level of care
Hospital center	179	1,313.51	502	580.05	1.895	1.718	2.091	<0.001	3	22.01	5	5.78	3.359	1.779	6.348	<0.001
Regional hospital	233	1,172.03	540	494.49	1.984	1.798	2.188	<0.001	4	20.12	16	14.65	1.211	0.641	2.288	0.682
Local hospital	149	1,152.72	450	532.79	1.811	1.641	1.998	<0.001	7	54.15	12	14.21	3.360	1.779	6.350	<0.001

PYs = Person-years; Rate: per 10⁵ PYs; Adjusted HR = Adjusted Hazard ratio: Adjusted for the variables listed in Table 3.; CI = Confidence interval