Table 1 Baseline characteristics of the two cohorts in fresh ET and FET cycles

Age

29.5 ± 3.9

29.8 ± 4.2

30.7 ± 4.9

30.2 ± 4.8

0.001*

3.20

<35

1094 (91.5)

1406 (89.2)

913 (71.6)

1586 (73.0)

0.698

0.70

≥35

102 (8.5)

117 (10.8)

362 (28.4)

587 (27.0)

BMI

22.9 ± 3.0

23.0 ± 3.1

23.0 ± 2.5

22.8 ± 2.3

0.016*

2.42

Infertile year

1.8 ± 1.3

1.8 ± 1.8

2.5 ± 1.5

2.7 ± 1.5

0.001*

3.23

Cause of infertility

0.177

0.82

Tubal factor

788 (65.9)

1067 (67.7)

826 (64.8)

1458 (67.1)

Male factor

408 (34.1)

509 (32.3)

449 (35.2)

715 (32.9)

Current cycle

1.4 ± 0.7

1.4 ± 1.1

2.4 ± 1.8

2.4 ± 1.6

0.194

1.30

bFSH

7.0 ± 2.2

7.0 ± 3.7

7.9 ± 2.6

7.7 ± 1.8

0.057

1.91

bE2

37.1 ± 8.9

36.5 ± 9.1

48.7 ± 16.0

49.5 ± 12.4

0.146

−1.45

bLH

4.6 ± 3.3

4.3 ± 2.8

4.4 ± 2.5

4.3 ± 2.1

0.201

1.28

PRL

414.7 ± 178.8

402.0 ± 204.8

4.9.3 ± 254.9

409.9 ± 184.8

0.939

−0.077

AMH

5.4 ± 0.60

5.3 ± 0.67

5.1 ± 2.6

5.3 ± 2.8

0.068

−1.824

AFC

15.7 ± 4.4

15.5 ± 5.4

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Number of oocytes retrieved

10.5 ± 4.5

10.6 ± 3.9

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Number of available embryos

8.2 ± 1.2

8.0 ± 1.6

/

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Number of high-quality embryos

5.1 ± 2.6

4.8 ± 2.4

/

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embryo stage

0.01*

6.57

cleavage-stage embryo

1015 (84.9)

1040 (66.0)

874 (68.5)

1395 (64.2)

blastocyst

181 (15.1)

536 (34.0)

401 (31.4)

778 (35.8)

endometrial thickness at the day of transplantation

11.6 ± 1.3

11.7 ± 1.1

10.3 ± 1.9

10.2 ± 1.5

0.091

1.69

mode of delivery

0.000*

210.9

cesarean section

766 (64.0)

1233 (78.2)

851 (66.7)

1899 (87.4)

vaginal delivery

430 (36.0)

343 (21.8)

424 (33.3)

274 (12.6)