Table 1 Comparison of baseline characteristics and pregnancy outcomes between non-RIF patients and RIF patients.

Female age (year)

32.53 ± 4.44

33.79 ± 4.50

 < 0.001

Infertility duration (year)

5.09 ± 3.13

5.80 ± 3.31

 < 0.001

Infertility type

Primary

47.6% (974/2045)

50.7% (791/1560)

0.069

Secondary

52.4% (1071/2045)

49.3% (769/1560)

Infertility factors

Pelvic and tubal factors

55.9% (1144/2045)

56.8% (886/1560)

0.126

Male factor

19.3% (394/2045)

20.4% (318/1560)

ovulatory dysfunction

14.0% (287/2045)

11.6% (181/1560)

Endometriosis

4.6% (95/2045)

5.7% (89/1560)

Others

6.1% (125/2045)

5.5% (86/1560)

BMI (kg/m²)

23.17 ± 3.80

22.96 ± 3.16

0.074

Basal serum FSH (IU/L)

7.28 ± 2.58

7.65 ± 2.84

 < 0.001

Basal LH (IU/L)

4.62 ± 2.40

4.53 ± 2.22

0.254

Basal serum PRL (ng/ml)

13.34 ± 7.53

13.54 ± 7.50

0.434

Basal serum E2 (pg/mL)

46.39 ± 29.38

45.62 ± 28.64

0.440

Basal serum T (ng/ml)

0.49 ± 0.35

0.47 ± 0.42

0.125

AMH (ng/ml)

4.30 ± 3.77

4.20 ± 3.73

0.444

Endometrial thickness on progesterone initiation day (mm)

9.79 ± 2.03

9.81 ± 2.08

0.843

Number of embryos transferred per ET

1.63 ± 0.50

1.61 ± 0.52

0.357

Embryo stage

D3 cleavage-stage embryos (%)

78.9% (1614/2045)

83.1% (1296/1560)

0.002

D5 or D6 blastocysts (%)

21.1% (431/2045)

16.9% (264/1560)

NO. of previous failed ET cycle

1.00 ± 0

2.51 ± 0.86

 < 0.001