Table 1.
Baseline characteristics of the study population
| Characteristics | Total=15 969 | Preterm delivery | Term delivery |
| n=3335 (exposed group) | n=12 634 (control group) | ||
| Age at delivery, Mean (SD), y |
30.8 (SD 6.0) | 30.7 (SD 5.9) | |
| Ethnicity n (%) |
White | 1592 (47.7) | 5711 (45.2) |
| Black | 185 (5.6) | 544 (4.3) | |
| South Asian | 133 (4.0) | 328 (2.6) | |
| Others | 101 (3.0) | 300 (2.4) | |
| Missing values | 1324 (39.7) | 5751 (45.5) | |
| BMI (kg/m2) n (%) |
Mean (SD) | 25.8 (SD 5.9) | 25.5 (SD 5.5) |
| < 18.5 (underweight) | 131 (3.9) | 374 (3.0) | |
| 18.5 to 24.9 (normal) | 1431 (42.9) | 5698 (45.1) | |
| 25 to 29.9 (overweight) | 750 (22.5) | 2861 (22.7) | |
| >30 (obese) | 621 (18.6) | 1895 (15.0) | |
| Missing values | 402 (12.1) | 1806 (14.3) | |
| Smoking status n (%) |
Never | 1807 (54.2) | 7183 (56.9) |
| Former | 549 (16.5) | 2040 (16.2) | |
| Current | 816 (24.5) | 2714 (21.5) | |
| Missing values | 163 (4.9) | 697 (5.5) | |
| Baseline hypertension n (%) |
Normotensive | 3177 (95.3) | 12 429 (98.4) |
| Chronic hypertension | 64 (1.9) | 97 (0.8) | |
| HDP | 94 (2.8) | 108 (0.9) | |
| Baseline diabetes n (%) |
Non-diabetes | 3151 (94.5) | 12 303 (97.4) |
| Pregestational type 1 DM | 40 (1.2) | 43 (0.3) | |
| Pregestational type 2 DM | 13 (0.4) | 31 (0.3) | |
| GDM | 131 (3.9) | 257 (2.0) | |
| Current lipid-lowering medication, n (%) | 16 (0.5) | 38 (0.3) | |
| Cardiovascular diseases, n (%) | 14 (0.4) | 41 (0.3) | |
| Migraine, n (%) | 422 (12.7) | 1182 (9.4) | |
| Polycystic ovarian syndrome, n (%) | 131 (3.9) | 420 (3.3) | |
| Sexually transmitted diseases, n (%) | 10 (0.3) | 33 (0.3) | |
| Chronic inflammatory diseases, n (%) | 75 (2.3) | 252 (2.0) | |
| Reproductive tumour, n (%) | 37 (1.1) | 80 (0.6) | |
Reproductive tumours (uterine fibroids, gynaecological cancer), sexually transmitted diseases (syphilis, hepatitis C, HIV infection), chronic inflammatory diseases (adenomyosis, endometriosis, interstitial cystitis), cardiovascular diseases (ischaemic heart disease, heart failure, myocardial infarction, peripheral vein disease, stroke, transient ischaemic attack).
BMI, Body Mass Index; DM, diabetes mellitus; GDM, gestational diabetes mellitus; HDP, hypertensive disorder in pregnancy.