(part 1 of 2): Characteristics of study population
| Characteristic | No. (%) of pregnancies* | p value† | |
|---|---|---|---|
| Cases n = 8702 | Controls n = 87 020 | ||
| Gestational age at index date,‡ wk | 14.1 ± 3.1 | 14.1 ± 3.1 | 0.9 |
| As of first day of gestation | |||
| Age, yr, mean ± SD | 28.7 ± 6.3 | 27.8 ± 5.5 | < 0.001 |
| Age group, yr | |||
| 18–34 | 6732 (77.3) | 73 947 (84.9) | < 0.001 |
| < 18 | 145 (1.6) | 1410 (1.6) | 0.7 |
| > 34 | 1825 (20.9) | 11 663 (13.4) | < 0.001 |
| Urban residence | 7237 (83.1) | 71 754(82.4) | 0.09 |
| Recipient of social assistance | 2337 (26.8) | 22 390 (25.7) | 0.02 |
| Education (≤ 12 yr) | 3773 (43.3) | 37 309 (42.8) | 0.4 |
| Living alone | 1554 (17.8) | 13 557 (15.5) | < 0.001 |
| In year before and during pregnancy until index date‡ | |||
| Chronic comorbidity or maternal infection | |||
| Depression§ | 1806 (20.7) | 12 508 (14.3) | < 0.001 |
| Asthma§ | 1418(16.3) | 11 319 (13.0) | < 0.001 |
| Diabetes mellitus§ | 176 (2.0) | 1625 (1.8) | 0.3 |
| Chronic hypertension§ | 228 (2.6) | 1946 (2.2) | 0.02 |
| Thyroid disorder§ | 348 (4.0) | 3216 (3.7) | 0.2 |
| Epilepsy§ | 204 (2.3) | 1130 (1.3) | < 0.001 |
| Endometriosis¶ | 106 (1.2) | 558 (0.6) | < 0.001 |
| Uterine malformations¶ | 6 (< 0.1) | 25 (< 0.1) | 0.06 |
| Rheumatoid polyarthritis and systemic lupus erythematosus§ | 2 (< 0.1) | 43 (< 0.1) | 0.3 |
| Urinary tract infection¶ | 1158 (13.3) | 9702 (11.1) | < 0.001 |
| Respiratory tract infection¶ | 2847 (32.7) | 24 857 (28.5) | < 0.001 |
| Bacterial vaginosis¶ | 884(10.1) | 7311 (8.4) | < 0.001 |
| Sexually transmitted infection¶ | 357(4.1) | 3289 (3.7) | 0.1 |
| Medication use | |||
| Other anti-infectives** | 860 (9.8) | 7056 (8.1) | < 0.001 |
| In year before pregnancy | |||
| Health care utilization | |||
| Hospital admission or emergency department visit | 3285 (37.7) | 29 030 (33.3) | < 0.001 |
| No. of physician visits | |||
| 0 | 2289 (26.3) | 25 956 (29.8) | < 0.001 |
| 1–2 | 1728 (19.8) | 18 936 (21.7) | < 0.001 |
| ≥3 | 4685 (53.8) | 42 128 (48.4) | < 0.001 |
| Medication use | |||
| Antibiotics | 3560 (40.9) | 31 576 (36.2) | < 0.001 |
| Drugs other than anti-infectives | |||
| 0 | 2216 (25.4) | 25 730 (29.5) | < 0.001 |
| 1–2 | 1720 (19.7) | 18 107 (20.8) | 0.02 |
| ≥ 3 | 4766 (54.7) | 43 183 (49.6) | < 0.001 |
| History of obstetric complications | |||
| Prior spontaneous abortion | 135 (1.5) | 856 (0.9) | < 0.001 |
| Prior abortion | 562 (6.4) | 3645 (4.1) | < 0.001 |
| Antibiotic use during pregnancy | 1428 (16.4) | 11 018 (12.6) | < 0.001 |
| Cephalosporins†† | 60 (0.69) | 622 (0.71) | |
| Penicillins†† | 500 (5.75) | 5573 (6.40) | |
| Macrolides†† | 264 (3.03) | 1525 (1.75) | |
| Quinolones†† | 160 (1.84) | 529 (0.61) | |
| Sulfonamides†† | 30 (0.34) | 139 (0.16) | |
| Tetracyclines†† | 67 (0.77) | 248 (0.28) | |
| Other antibacterials†† | 34 (0.39) | 278 (0.32) | |
| Antiprotozoals†† | 53 (0.61) | 291 (0.33) | |
| Urinary anti-infectives†† | 39 (0.45) | 562 (0.65) | |
| Use of ≥ 2 classes of antibiotics‡‡ | 221 (2.54) | 1251 (1.44) | < 0.001 |
Note: SD = standard deviation.
↵* Unless stated otherwise.
↵† Pearson χ2 test for categorical variables and t test for continuous variables.
↵‡ Index date = date of spontaneous abortion for cases and corresponding date for matched controls.
↵§ Based on ICD-9 or ICD-10 codes or prescriptions filled for chronic diseases (depression, asthma, diabetes mellitus, chronic hypertension, thyroid disorder, epilepsy, and rheumatoid polyarthritis and systemic lupus erythematosus).
↵¶ Based on ICD-9 or ICD-10 codes for urinary tract infections, respiratory tract infections, bacterial vaginosis, endometriosis, sexually transmitted infection and uterine malformations.
↵** Includes prescriptions for anti-infectives other than antibiotics (e.g., antituberculosis drugs, antifungals, antivirals, antimalarial, highly active antiretroviral therapy, anthelmintics, amebicides).
↵†† Includes prescriptions for at least one dose of only this class of antibiotic between first day of gestation and index date.
↵‡‡ Includes prescriptions for at least one dose of ≥ 2 different classes of antibiotic between first day of gestation and index date.