Covariate Statistics OR (95%CI) P-value
Female age at oocyte retrieval (y) 30.58 ± 4.91 0.92 (0.91, 0.92) <0.001
Female age at embryo transfer (y) 31.03 ± 4.84 0.92 (0.91, 0.92) <0.001
Infertility duration (y) 3.46 ± 2.89 0.97 (0.95, 0.98) <0.001
BMI (kg/m2)
<18.5 (n, %) 862 (9.40%) Reference
18.5-25 (n, %) 6740 (73.52%) 0.96 (0.83, 1.10) 0.553
>25 (n, %) 3065 (33.44%) 0.77 (0.65, 0.91) 0.003
AFC (n) 12.63 ± 5.98 1.05 (1.04, 1.06) <0.001
No. of oocyte retrieved (n) 13.48 ± 7.47 1.05 (1.04, 1.05) <0.001
Fertilization type (n, %)
   IVF 6829 (73.62%) Reference
   ICSI 2191 (23.62%) 1.08 (0.98, 1.19) 0.106
IVF+ICSI 256 (2.76%) 1.04 (0.81, 1.34) 0.749
Infertility type (n, %)
   Primary infertility 4878 (53.08%) Reference
   Secondary infertility 4312 (46.92%) 0.71 (0.65, 0.77) <0.001
Protocol in the fresh cycle (n, %)
   Agonist 6853 (74.10%) Reference
   Antagonist 1844 (19.94%) 0.57 (0.52, 0.64) <0.001
Other 551 (5.96%) 0.38 (0.32, 0.46) <0.001
Previous fresh embryo transfer (n, %) 4599(47.23) 0.81(0.73,0.96) 0.082
Clinical pregnancy in fresh cycles (n, %) 2561(55.69) 0.92(0.83,1.01) 0.097
Single blastocyst transfer (n, %)
No 7825 (80.40) Reference
Yes 1908 (19.60) 0.74 (0.67, 0.82) <0.001
Endometrial thickness on the day of P administration (mm) 10.15 ± 1.66 1.07 (1.04, 1.09) <0.001
Triple-line endometrial pattern (n, %)
   A 1414 (14.55) Reference
   B 7662 (78.84) 0.91 (0.81, 1.02) 0.102
   C 643 (6.62) 0.63 (0.52, 0.76) <0.001
Type of embryo transferred (n, %)
   Cleavage stage 4201 (43.16) Reference
   Blastocyst stage 5532 (56.84) 1.61 (1.48, 1.74) <0.001
No. of transferred embryos (n, %)
   1 2587 (26.58) Reference
   2 7023 (72.16) 1.80 (1.64, 1.97) <0.001
3 123 (1.26) 0.74 (0.51, 1.09) 0.129
No. of transferrable embryos (n) 7.08 ± 4.34 1.10 (1.08, 1.11) <0.001
No. of good quality embryos transferred (n, %)
0 3430 (35.24) Reference
1 3643 (37.43) 1.68 (1.53, 1.85) <0.001
2 2659 (27.30) 2.89 (2.60, 3.22) <0.001