Table 2.

 Univariate logistic regression analyses of different variables with SSR

Variables	Total births	Male babies	SSR(%)	OR	95%CI
Number of cycles
1 ~ 3	2519	1272	50.50	1.000
4 ~ 6	29	13	44.83	0.797	0.382–1.663
Maternal age group
20 ~ 29	892	441	49.44	1.000
30 ~ 39	1610	818	50.81	1.056	0.897–1.244
≥ 40	46	26	56.52	1.329	0.731–2.417
Paternal age group
20 ~ 29	660	326	49.39	1.000
30 ~ 39	1661	839	50.51	1.046	0.873–1.25
40 ~ 49	213	117	54.93	1.249	0.916–1.703
50 ~ 59	14	3	21.43	0.279	0.077–1.011
Infertility duration
0 ~ 10	2433	1222	50.23	1.000
11 ~ 20	115	63	54.78	1.201	0.825–1.748
Maternal BMI
18.5 ~ 25	1723	876	50.58	1.000
< 18.5	593	286	48.23	0.901	0.747–1.086
≥ 25	232	123	53.02	1.091	0.829–1.436
Infertility type
Primary	1766	898	50.85	1.000
Secondary	782	387	49.49	0.947	0.800-1.121
Infertility factor
Male	987	483	48.94	1.000
Female	989	510	51.57	1.111	0.931–1.325
Both male and female	368	183	49.73	1.032	0.812–1.311
Unknown	204	109	53.43	1.197	0.885–1.619
Fertilization method
IVF	1544	800	51.81	1.000
ICSI	822	380	46.23	0.800	0.675–0.947
R-ICSI	182	105	57.69	1.268	0.930–1.730
Embryo transfer morphology
Fresh	656	341	51.98	1.000
Thawed	1892	944	49.89	0.920	0.770–1.099
Number of embryos transferred
1	214	117	54.67	1.000
2	2288	1149	50.22	0.836	0.631–1.108
3	46	19	41.30	0.583	0.306–1.113
Embryo transfer stage
Blastocyst	551	283	51.36	1.000
Cleavage stage	1997	1002	50.18	0.954	0.790–1.152
Birth type
Singletons	2119	1060	50.02	1.000
Twins	429	225	52.45	1.102	0.895–1.356