Table 1 Demographic characteristics of participants

Age (years)

30.9 ± 4.4

30.4 ± 4.6

31.7 ± 4.5

30.5 ± 3.9

31.2 ± 4.7

0.546

–

–

–

–

–

–

Height (cm)

158.5 ± 5.7

160.4 ± 6.3

158.7 ± 4.8

159.0 ± 5.7

157.4 ± 5.5

0.073

–

–

–

–

–

–

Weight before pregnancy (kg)

52.9 ± 7.6

54.5 ± 8.8

53.5 ± 8.3

52.5 ± 6.9

52.4 ± 7.4

0.542

–

–

–

–

–

–

Weight [during experimental period] (kg)

59.9 ± 7.8

61.7 ± 7.5

60.7 ± 9.7

59.8 ± 7.3

59.1 ± 7.7

0.436

56.1 ± 7.6

57.7 ± 7.8

57.3 ± 9.5

56.0 ± 6.9

55.2 ± 7.5

2.079

 0 (primiparity)

83

9 (28.1)

8 (38.1)

33 (47.8)

33 (41.8)

–

–

–

–

–

–

–

 1

83

18 (56.3)

6 (28.6)

27 (39.1)

32 (40.5)

–

–

–

–

–

–

–

 2

28

5 (15.6)

7 (33.3)

5 (7.2)

11 (13.9)

–

–

–

–

–

–

–

 3

5

0 (0)

0 (0)

4 (5.8)

1 (1.3)

–

–

–

–

–

–

–

 4

1

0 (0)

0 (0)

0 (0)

1 (1.3)

–

–

–

–

–

–

–

 5

1

0 (0)

0 (0)

0 (0)

1 (1.3)

–

–

–

–

–

–

–

Average (number)

0.8 ± 0.9

0.9 ± 0.7

1.0 ± 0.9

0.7 ± 0.8

0.8 ± 1.0

0.630

–

–

–

–

–

–

Anterior pelvic width (cm)

24.9 ± 2.4

25.4 ± 2.6

24.1 ± 1.9

24.8 ± 2.6

25.0 ± 2.4

0.305

23.7 ± 2.6

24.5 ± 3.0

23.6 ± 2.9

23.8 ± 2.5

23.4 ± 2.5

0.211

Anterior pelvic width [divided by height] (cm/m)

15.7 ± 1.5

15.8 ± 1.5

15.2 ± 1.1

15.6 ± 1.5

15.9 ± 1.6

0.251

15.0 ± 1.6

15.3 ± 1.9

14.9 ± 1.7

15.0 ± 1.5

14.9 ± 1.6

0.608

Posterior pelvic width (cm)

11.6 ± 3.5

12.1 ± 3.8

10.2 ± 3.4

11.6 ± 3.3

11.8 ± 3.6

0.224

11.5 ± 3.7

11.9 ± 4.4

9.6 ± 2.8 ^†1

12.1 ± 4.2 ^†1

11.2 ± 2.7

0.040

Posterior pelvic width [divided by height] (cm/m)

7.3 ± 2.3

7.5 ± 2.3

6.4 ± 2.1

7.3 ± 2.0

7.6 ± 2.5

0.193

7.2 ± 2.3

7.4 ± 2.8

6.1 ± 1.7 ^†2

7.6 ± 2.6 ^†2

7.1 ± 1.8

0.046

Pelvic asymmetry (°)

3.0 ± 3.0

4.2 ± 4.3

2.9 ± 3.0

2.7 ± 2.7

2.7 ± 2.4

0.080

3.0 ± 3.8

2.0 ± 1.9

2.1 ± 1.8

3.9 ± 4.9

2.8 ± 3.5

0.062

 Natural childbirth

157

29 (90.6)

16 (76.2)

55 (79.7)

55 (69.6)

0.107

–

–

–

–

–

–

 Cesarean section

28

3 (9.4)

3 (14.3)

10 (14.5)

14 (17.7)

0.734

–

–

–

–

–

–

 Forceps delivery

8

0 (0)

1 (4.8)

2 (2.9)

5 (6.3)

0.438

–

–

–

–

–

–

 Vacuum extraction

5

0 (0)

1 (4.8)

1 (1.4)

3 (3.8)

0.546

–

–

–

–

–

–

 Epidural

3

0 (0)

0 (0)

1 (1.4)

2 (2.5)

0.709

–

–

–

–

–

–

Duration of labor [excluding cesarean section] (minute)

472.1 ± 377.8

489.5 ± 374.1

491.9 ± 392.1

501.0 ± 432.0

433.6 ± 326.6

0.779

–

–

–

–

–

–

Birth weight (kg)

3.1 ± 0.4

3.0 ± 0.6

3.0 ± 0.3

3.2 ± 0.4

3.0 ± 0.4

0.096

–

–

–

–

–

–