Characteristics of the study population
| Characteristic | No. (%) of pregnancies* | Standardized mean difference† | p value‡ | |
|---|---|---|---|---|
| Term delivery (≥ 37 wk) n = 53 947 | Preterm delivery (< 37 wk) n = 3677 | |||
| Pregnancy characteristics | ||||
| Pregnancies conceived spontaneously | 52 074 (96.5) | 3495 (95.1) | −0.07 | |
| Pregnancies conceived through use of OS and ART | 1873 (3.5) | 182 (5.0) | 0.07 | < 0.001 |
| OS alone | 381 (0.7) | 38 (1.0) | 0.03 | |
| ART alone | 135 (0.2) | 15 (0.4) | 0.03 | |
| OS and ART combined | 1357 (2.5) | 129 (3.5) | 0.06 | < 0.001 |
| Maternal and child sociodemographic characteristics§ | ||||
| Maternal | ||||
| Maternal age, yr, mean ± SD | 29.14 ± 5.6 | 29.23 ± 6.0 | −0.02 | < 0.001 |
| Maternal age, yr | ||||
| < 25 | 12 096 (22.4) | 865 (23.5) | 0.03 | |
| 25–35 | 32 077 (59.5) | 2047 (55.7) | −0.08 | |
| 35–40 | 7931 (14.7) | 586 (15.9) | 0.03 | |
| ≥ 40 | 1843 (3.4) | 179 (4.9) | 0.07 | < 0.001 |
| Recipient of social assistance | 9848 (18.2) | 997 (27.1) | 0.21 | < 0.001 |
| Urban dweller | 44 667 (82.8) | 3008 (81.8) | −0.03 | 0.12 |
| Child | ||||
| Sex, male | 27 581 (51.1) | 2038 (55.4) | 0.09 | < 0.001 |
| Birth weight, g, mean ± SD | 3401.90 ± 455.56 | 2412.44 ± 648.78 | 2.10 | < 0.001 |
| Pregnancies conceived spontaneously | 3402.15 ± 455.33 | 2418.47 ± 643.11 | ||
| Pregnancies conceived through use of OS or ART or both | 3394.13 ± 462.45 | 2296.56 ± 741.81 | ||
| Maternal comorbidities¶ | ||||
| Diabetes | 1536 (2.8) | 124 (3.4) | 0.03 | 0.07 |
| Hypertension | 1118 (2.1) | 88 (2.4) | 0.02 | 0.19 |
| Obesity | 1270 (2.4) | 104 (2.8) | 0.03 | 0.07 |
| Asthma | 4771 (8.8) | 358 (9.7) | 0.03 | 0.07 |
| Epilepsy | 619 (1.2) | 53 (1.4) | 0.03 | 0.11 |
| Smoking | 1054 (2.0) | 81 (2.2) | 0.02 | 0.29 |
| Infection | 15 847 (29.4) | 1076 (29.3) | 0.00 | 0.89 |
| Thyroid disease | 3123 (5.8) | 236 (6.4) | 0.03 | 0.12 |
| Depression or anxiety | 6912 (12.8) | 513 (14.0) | 0.03 | 0.05 |
| Coagulopathy | 221 (0.4) | 22 (0.6) | 0.03 | 0.09 |
| Previous pregnancy | 6382 (11.8) | 477 (13.0) | 0.03 | 0.04 |
| Delivery | 2175 (4.0) | 140 (3.8) | ||
| Abortion | 2609 (4.8) | 199 (5.4) | ||
| Miscarriage | 1598 (3.0) | 138 (3.8) | ||
| No. of any other medications used** | ||||
| 0 | 19 735 (36.6) | 1292 (35.1) | −0.09 | |
| 1 | 10 529 (19.5) | 753 (20.5) | 0.02 | |
| 2 or 3 | 12 980 (24.1) | 889 (24.2) | 0.00 | |
| ≥ 4 | 10 703 (19.8) | 743 (20.2) | 0.01 | 0.28 |
| Pregnancy complications | ||||
| Premature rupture of membranes | 2994 (5.6) | 222 (6.0) | 0.02 | 0.21 |
| Placental dysfunction | 280 (0.5) | 26 (0.7) | 0.02 | 0.13 |
| Preterm labour | 526 (1.0) | 46 (1.2) | 0.03 | 0.10 |
| Bleeding | 1291 (2.49) | 105 (2.9) | 0.03 | 0.08 |
| Utilization of health care services | ||||
| Follow-up by obstetrician‡‡ | 31 066 (57.6) | 2121 (57.7) | 0.002 | 0.91 |
| Follow-up by general practitioner or family physician‡‡ | 13 354 (24.8) | 891 (24.2) | −0.01 | 0.48 |
| Hospital admission and/or visit to emergency department§§ | 20 725 (38.4) | 1399 (38.0) | −0.01 | 0.66 |
Note: ART = assisted reproductive technologies, OS = ovarian stimulators, SD = standard deviation.
↵* Unless indicated otherwise.
↵† Standardized mean differences ≥ 0.10 represent a clinically significant difference between groups.
↵‡ p values were calculated to compare term births with preterm births using Pearson χ2 tests for categorical variable and t tests for continuous variables.
↵§ Measured at the first day of gestation.
↵¶ Measured in the 12 mo before the first day of gestation. Diagnoses are based on International Classification of Diseases and Related Health Problems, 10th Revision, codes or a filled prescription or both in relation to the comorbidity.
↵** Excludes all prescriptions filled for comorbidities listed above.
†† Defined as ≥ 5 visits over the course of the pregnancy.
↵‡‡ In the 12 mo before the first day of gestation.