Table 1 Baseline characteristics of all transfer cycles

Maternal age (years)

34.88 ± 5.57

34.43 ± 5.53

0.253

Parental age (years)

36.46 ± 6.47

36.06 ± 6.26

0.383

Maternal BMI (kg/m²)

22.27 ± 5.88

22.01 ± 3.22

0.262

Duration of infertility (years)

3.22 ± 3.19

3.43 ± 3.00

0.344

Primary infertility (n,%)

2995/5873 (51.00%)

243/414 (58.70%)

0.003*

Pluriparous (n,%)

979/5873 (16.67%)

63/414 (15.22%)

0.494

Type of FET cycles

0.074

Natrual

836/5873 (14.23%)

51/414 (12.32%)

 HRT

2562/5873 (43.62%)

165/414 (39.86%)

 OS

2475/5873 (42.14%)

198/414 (47.83%)

Insemination method of embryos

< 0.001*

 IVF

3790/5873 (64.53%)

230/414 (55.56%)

 ICSI

2083/5873 (35.47%)

184/414 (44.44%)

Endometrial thickness (mm)

10.42 ± 2.38

10.67 ± 2.56

0.125

Basal FSH (mIU/ml)

5.86 (4.81–7.72)

5.54 (4.53–7.18)

0.052

Basal LH (mIU/ml)

4.48 ± 4.25

4.47 ± 3.76

0.974

Basal E2 (pg/ml)

47.33 ± 47.13

44.11 ± 35.79

0.355

Basal P4 (ng/ml)

0.20 (0.20–0.30)

0.20 (0.20–0.30)

0.526