Table 1 Distribution of potential confounders (N = 1702)
| Â | N (%) |
|---|---|
Pre-pregnancy BMI | |
 Normal | 1287/1496 (86.0%) |
 Overweight | 170/1496 (11.4%) |
 Obese | 39/1496 (2.6%) |
Smoking status (obtained at, or before, the first clinic) | |
 Never smoker | 809/1483 (54.6%) |
 Former smoker | 525/1483 (35.4%) |
 Current smoker | 149/1483 (10.0%) |
Alcohol intake frequency (obtained at, or before, the first clinic) | |
 Never or less than 4 times a month | 468/1155 (40.5%) |
 2 to 3 times a week | 384/1155 (33.2%) |
 4 or more times a week | 303/1155 (26.2%) |
Parity | |
 1 | 193/1702 (11.3%) |
 2 | 567/1702 (33.3%) |
 3 | 423/1702 (24.9%) |
 4+ | 518/1702 (30.5%) |
Age at menarche (taken at time of recruitment to the study (mean age 28.3, SD 4.8)) | |
 Early (≤ 11 years) | 242/1507 (16.1%) |
 Average (12-14 years) | 1055/1507 (70.0%) |
 Late (≥ 15 years) | 210/1507 (13.9%) |
Educational achievement (taken at time of recruitment to the study (mean age 28.3, SD 4.8)) | |
 CSE/vocational degree/ O-level | 688/1587 (43.4%) |
 A-level | 498/1587 (31.4%) |
 University degree | 401/1587 (25.3%) |