Table 1 Baseline characteristics of all FET cycles

Age of embryo transfer (years), mean (SD),

32.82 ± 3.40

33.09 ± 3.81

33.27 ± 3.61

0.152

0.542

0.076

Duration of infertility (years), mean (SD)

3.80 ± 2.39

4.02 ± 2.80

4.21 ± 3.04

0.114

0.412

0.058

BMI of women, mean (SD)

21.45 ± 1.72

26.93 ± 2.21

32.13 ± 1.89

< 0.0001

< 0.0001

< 0.0001

Antral follicle count, mean (SD)

18.48 ± 6.23

18.85 ± 6.96

17.78 ± 8.01

0.306

0.069

0.218

0.075

0.968

0.727

 PCOS only

266 (27.38%)

123 (25.72%)

59 (25.99%)

 PCOS + male factor

120 (12.32%)

55 (11.45%)

28 (12.19%)

 PCOS + tubal factor

486 (49.97%)

242 (50.34%)

115 (50.62%)

 PCOS + male factor + tubal factor

74 (7.69%)

33 (6.93%)

16 (7.21%)

 PCOS + other factor

26 (2.64%)

27 (5.56%)

10 (3.99%)

Basal FSH (mIU/mL), median (min-max)

5.21 (0.32–9.98)

4.94 (0.26–9.99)

4.61 (0.45–9.99)

< 0.0001

0.031

0.002

Basal LH (mIU/mL),median (min-max)

5.36 (0.19–18.92)

4.57 (0.16–17.29)

4.02 (0.28–18.49)

< 0.0001

0.031

< 0.0001

Basal E2 (pg/mL),median (min-max)

36.00 (10.00–84.00)

37.00 (10.00–90.00)

37.00 (10.00–88.00)

0.546

0.929

0.618

Basal P (ng/mL),median (min-max)

0.30 (0.10–0.80)

0.30 (0.10–0.90)

0.30 (0.10–0.90)

< 0.0001

0.032

< 0.0001

Previous IVF failures n (%)

0.177

0.941

0.585

 0

693 (71.28%)

361 (75.17%)

169 (73.96%)

 1–2

207 (21.28%)

94 (19.52%)

46 (19.99%)

  ≥ 3

72 (7.44%)

25 (5.31%)

13 (6.05%)

Type of infertility, n (%)

0.155

0.163

0.754

 Primary

652 (67.04%)

335 (69.72%)

156 (68.23%)

 Secondary

320 (32.96%)

145 (30.28%)

72 (31.77%)

Type of FET cycle

0.112

0.073

0.062

 HRT

399 (41.07%)

217 (45.16%)

107 (46.93%)

 Ovarian stimulation

573 (58.93%)

263 (54.84%)

121 (53.07%)

Endometrial thickness [17]

11.28 ± 2.02

11.32 ± 2.05

11.29 ± 1.98

0.532

0.329

0.835

Fertilization method,n (%)

0.523

0.822

0.894

 IVF

562 (57.85%)

287 (59.71%)

131 (57.29%)

 ICSI

222 (22.82%)

97 (20.27%)

50 (21.96%)

 Half IVF + half ICSI

188 (19.33%)

96 (20.02%)

47 (20.75%)