Table 1 Sample size calculations
From: Maternal health study: a prospective cohort study of nulliparous women recruited in early pregnancy
Exposure comparison (ratio of unexposed: exposed) | Outcome of interest | Difference | Sample size estimate | Total number required* |
|---|---|---|---|---|
Spontaneous vaginal birth:forceps/vacuumextraction (2:1) | Urinary incontinence Faecal incontinence Sexual problems Perineal pain | 11% versus 18% 2.6% versus 8% 24% versus39% 20% versus 53% | 930 642 360 168 | 1200 800 450 210 |
Emergency caesarean:forceps/vacuum extraction (1:2) | Urinary incontinence Faecal incontinence Sexual problems | 7% versus 18% 3.9% versus 10.5% 29% versus 39% | 371 573 841 | 950 1500 2200 |
Elective caesarean:forceps/vacuum extraction (1:5) | Urinary incontinence Faecal incontinence Sexual problems | 2.4% versus 18% 2.8% versus 10.5% 27% versus 39% | 276 763 938 | 900 2500 3100 |