Formation of the two first-birth cohorts of women, for the comparison between eras
| Cohort 1 1994–1997 | Cohort 2 2001–2004 | |
|---|---|---|
| All first-births | 138186 | 141863 |
| Minimum follow-up | 12 years | 5 years |
| No record of subsequent birth | 38830 (28.1%) | 52773 (37.2%) |
| Second birth >5 years later | 16230 (11.7%) | 3168 (2.2%) |
| Second birth within 5 years | 83126 | 85922 |
| Missing delivery data | 138 (0.2%) | 63 (0.1%) |
| Included in cohort | 82988 (60.1%) | 85859 (60.5%) |