Table 1 Characteristics of the study population.

Age (years)

 Mean ± SD

31.3 ± 5.4

31.9 ± 4.3

30.7 ± 4.6

31.3 ± 4.6

 Range (Min/Max)

22 (18/40)

18 (21/39)

20 (22/42)

24 (18/42)

Age categorised (n, %)

 < 26 years

5 (16.7)

4 (6.6)

7 (11.5)

16 (10.5)

 26 < 35 years

15 (50.0)

38 (62.3)

41 (67.2)

94 (61.8)

 ≥ 35 years

10 (33.3)

19 (31.2)

13 (21.3)

42 (27.6)

Race (n, %)

 Asian

0 (0.0)

1 (1.6)

0 (0.0)

1 (0.7)

 Caucasian

30 (100.0)

60 (98.4)

61 (100.0)

151 (99.3)

Weight (kg)

 Mean ± SD

73.3 ± 12.5

70.9 ± 11.4

68.1 ± 9.6

70.2 ± 11.0

 Range (Min/Max)

42 (54/96)

56 (49/105)

60 (48/108)

60 (48/108)

BMI (kg/m²)

 Mean ± SD

25.8 ± 4.2

25.3 ± 3.3

24.3 ± 3.4

25.0 ± 3.6

 Range (Min/Max)

16.2 (18.8/35.0)

18.9 (17.4/36.3)

15.6 (17.7/33.3)

18.9 (17.4/36.3)

Number of pregnancies (including the index one) (n)

 Median

2

1

1

1

 Range (Min/Max)

5 (1/6)

3 (1/4)

3 (1/4)

5 (1/6)

 Primipara/Multipara

7/23

42/19

46/15

95/57

Risk factors for Obstetric Anal Sphincter Injury from the index delivery (n, %)

 Prolonged second phase of delivery

0 (0.0)

6 (9.8)

10 (16.4)

16 (10.5)

 Foetal shoulder dystocia

0 (0.0)

1 (1.6)

0 (0.0)

1 (0.7)

 Birth weight of the neonate > 4 kg

4 (13.3)

5 (8.2)

6 (9.8)

15 (9.9)

 Induction of delivery with oxytocin

1 (3.3)

14 (23.0)

9 (14.8)

24 (15.8)

 Head circumference of the neonate ≥ 34 cm

17 (56.7)

39 (63.9)

49 (80.3)

105 (69.1)

Time between the index delivery and ONIRY examination (days)

 Median

2

11

28

14

 Range (Min/Max)

53 (1/54)

58 (0/58)

55 (1/56)

58 (0/58)

Time between the index delivery and EAUS examination (days)

 Median

2

11

28

14

 Range (Min/Max)

53 (1/54)

58 (0/58)

55 (1/56)

58 (0/58)