Table 1 Power calculations with n = 904** in each arm

%

%

Birth by caesarean section

19

14

Instrumental vaginal birth

10.6

6.6

Epidural analgesia

18

13

Intact perineum or unsutured laceration (increase)*

41.2

48.2

Intact perineum or unsutured laceration (decrease)*

41.2

34.2

3rd or 4th degree laceration* (would not miss this difference)

1.7

3.4

Induction of labour

27

21

Augmentation of labour

19

14

Exclusive breastfeeding at 6 months

8

12

Any breastfeeding at 6 months

53

63

Postnatal depression at 8 weeks

15

10

Postnatal depression at 6 months

15

10

Smoking at time of birth

15

10