Table 4 Baseline characteristics and pregnancy outcomes of patients with different stages of blastocysts transferred in two groups (\(\bar x\) ± s; %)

Age (yr)

31.78 ± 4.58

31.76 ± 4.52

31.40 ± 3.95

31.69 ± 4.41

BMI (kg/m²)

22.74 ± 3.34

22.77 ± 3.75

22.48 ± 3.10

22.34 ± 3.19

Infertility duration (yr)

3.74 ± 2.72

3.78 ± 2.85

3.44 ± 2.59

3.69 ± 2.70

AMH (ng/ml)

5.38 ± 4.64

5.70 ± 4.90

5.75 ± 4.35

5.76 ± 4.78

bFSH (mIU/ml)

6.82 ± 2.45

6.81 ± 4.13

6.55 ± 2.10

6.52 ± 3.00

Number of failed cycles

2.97 ± 1.76

3.16 ± 1.64

3.28 ± 1.53

3.33 ± 1.77

Endometrial thickness (mm)

10.94 ± 1.92

10.74 ± 2.08

10.92 ± 2.06

11.06 ± 2.26

High-quality embryos rate

41.3 (172/416)

45.1 (223/494)

37.7 (86/228)

42.5 (141/332)

Primary infertility rate

51.9 (108/208)

59.7 (129/216)

58.8 (87/148)

56.9 (82/144)

Infertility factors

Male factors

22.1 (46/208)

24.5 (53/216)

27.0 (40/148)

22.9 (33/144)

Tube and pelvic factors

42.3 (88/208)

43.1 (93/216)

41.9 (62/148)

37.5 (54/144)

Ovulatory factors

3.8 (8/208)

5.6 (12/216)

3.4 (5/148)

4.2 (6/144)

Couples’ factors

18.3 (38/208)

19.0 (41/216)

20.3 (30/148)

24.3 (35/144)

Others

13.5 (28/208)

7.9 (17/216)

7.4 (11/148)

11.1 (16/144)

Clinical pregnancy rate

24.5 (51/208)

33.8 (73/216)

17.6 (26/148)

28.5 (41/144)

Implantation rate

17.0 (60/416)

19.6 (97/494)

10.1 (30/296)

15.4 (51/332)

Multiple pregnancy rate

17.6 (9/51)

24.7 (18/73)

15.4 (4/26)

19.5 (8/41)

Miscarriage rate

11.8 (6/51)

12.3 (9/73)

15.4 (4/26)

14.6 (6/41)