Table 1 Characteristics of the modeling cohort and the external validation cohort

Age^a

32.77 (4.95)

32.73 (4.44)

34.25 (4.79)

30.72 (2.63)

Endometrial thickness^a

11.01 (1.95)

12.08 (2.71)

12.44 (2.78)

12.03 (3.15)

Endometrial volume^a

4.31 (1.40)

5.21 (1.81)

5.09 (2.07)

5.79 (2.72)

Endometrial morphology^c

 Type A

5(12.5%)

2 (6.1%)

0 (0.0%)

3 (16.7%)

 Type B

26 (65.0%)

28 (84.8%)

8 (66.7%)

13 (72.2%)

 Type C

9 (22.5%)

3 (9.1%)

4 (33.3%)

2 (11.1%)

Uterine artery mPI^a

2.18 (0.38)

2.12 (0.38)

1.97 (0.36)

2.05 (0.50)

Uterine artery mRI^a

0.81 (0.05)

0.80 (0.05)

0.78 (0.05)

0.79 (0.05)

Uterine artery mS/D^a

5.62 (1.44)

5.39 (1.38)

5.04 (1.39)

5.01 (1.01)

 VI^b

0.67 [0.21, 1.39]

1.05 [0.63, 2.95]

0.18 [0.16, 0.35]

1.34 [0.64, 3.53]

 FI^a

15.14 (3.00)

16.03 (3.91)

15.07 (3.86)

17.63 (3.23)

 VFI^a

0.09 [0.03, 0.21]

0.17 [0.07, 0.52]

0.03 [0.02, 0.04]

0.30 [0.11, 0.61]

Sub-endometrial blood flow^c

 Type I

18 (45.0%)

10 (30.3%)

8 (66.7%)

3 (16.7%)

 Type II

19 (47.5%)

20 (60.6%)

4 (33.3%)

12 (66.7%)

 Type III

3 (7.5%)

3 (9.1%)

0 (0.0%)

3 (16.7%)

Endometrial peristalsis^c

 Type I

6 (15.0%)

7 (21.2%)

1 (8.3%)

1 (5.6%)

 Type II

1 (2.5%)

1 (3.0%)

1 (8.3%)

1 (5.6%)

 Type III

2 (5.0%)

3 (9.1%)

0 (0.0%)

1 (5.6%)

 Type IV

0 (0.0%)

1 (3.0%)

0 (0.0%)

1 (5.6%)

 Type V

31 (77.5%)

21 (63.6%)

10 (83.3%)

14 (77.8%)