Table. Characteristics of the Study Population at the Time of IUD Insertion.
| Characteristic | Participants, No. (%) | |
|---|---|---|
| Full cohort (N = 326 658) | Subcohort with known breastfeeding status (n = 94 817)) | |
| Person-years at risk, No. | 641 427 | 182 738 |
| Breastfeeding | 64 186 (19.6) | 64 186 (67.7) |
| Postpartum time of IUD insertion | ||
| 0-3 d | 2788 (0.9) | 2647 (2.8) |
| 4 d to ≤6wk | 17 272 (5.3) | 16 933 (17.9) |
| >6 to ≤14 wk | 56 047 (17.2) | 54 697 (57.7) |
| >14 to ≤52 wk | 21 717 (6.6) | 20 540 (21.7) |
| Nonpostpartum (>52 wk or no delivery) | 228 834 (70.1) | NA |
| Age, y | ||
| Mean (SD) | 32.0 (8.3) | 29.3 (5.7) |
| ≤28 | 119 469 (36.6) | 40 360 (42.6) |
| >28 to ≤36 | 107 871 (33.0) | 44 643 (47.1) |
| >36 to ≤50 | 99 318 (30.4) | 9814 (10.4) |
| Race and ethnicitya | ||
| Asian/Pacific Islander | 38 911 (11.9) | 12 335 (13.0) |
| Hispanic | ||
| Black | 696 (0.2) | 208 (0.2) |
| Other | 56 180 (17.2) | 15 066 (15.9) |
| White | 42 501 (13.0) | 20 159 (21.3) |
| Non-Hispanic | ||
| Black | 28 323 (8.7) | 7255 (7.7) |
| White | 137 102 (42.0) | 34 092 (36.0) |
| Other or multiple | 16 357 (5.0) | 4741 (5.0) |
| Recent smokingb | 32 623 (10.0) | 7519 (7.9) |
| BMI | ||
| Mean (SD) | 28.5 (6.99) | 28.7 (6.18) |
| Categoryc | ||
| Underweight, <18.5 | 3689 (1.1) | 541 (0.6) |
| Normal weight, 18.5-24.9 | 113 675 (34.8) | 28 587 (30.1) |
| Overweight, 25.0-29.9 | 96 181 (29.4) | 32 628 (34.4) |
| Obesity, >30.0 | 107 674 (33.0) | 32 883 (34.7) |
| Dysmenorrhea in the past year | 15 266 (4.7) | 2249 (2.4) |
| Menorrhagia in the past year | 32 552 (10.0) | 898 (0.9%) |
| Uterine fibroids | 17 416 (5.3) | 3617 (3.8) |
| Parityd | ||
| ≤1 | 128 577 (39.4) | 31 789 (33.5) |
| >1 | 148 985 (45.6) | 57 376 (60.5) |
| Cesarean delivery any time before IUD insertione | 54 295 (16.6) | 25 792 (27.2) |
| Cesarean delivery for most recent delivery before IUD insertionf | 23 245 (7.1) | 22 551 (23.8) |
| IUD typeg | ||
| Levonorgestrel-releasing | 259 234 (79.4) | 72 201 (76.1) |
| Copper | 63 664 (19.5) | 22 004 (23.2) |
| Concomitant gynecological procedureh | 26 234 (8.0) | 1561 (1.6) |
| Indicator of difficult insertioni | 29 777 (9.1) | 2763 (2.9) |
| Annualized IUD insertions performed by clinician in previous year, mean (SD), No. | 52.0 (73.70) | 49.5 (79.52) |
| Duration of look-back period, mo | ||
| Mean (SD) | 56.8 (42.3) | 48.2 (35.0) |
| Median (IQR) [range] | 46.3 (26.1-76.6) [12-435] | 38.7 (23.0-64.2) [12-391] |
| Duration of follow-up, median (range), y | 1.4 (0.0-10.3) | 1.4 (0.0-10.3) |
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); NA, not applicable; IUD, intrauterine device.
Race and ethnicity were as reported in electronic health records. The other and unknown categories included both those who self-identified as other and groups with very small numbers in this study (eg, non-Hispanic Native American and non-Hispanic American Indian or Alaska Native). Unknown or missing: postpartum cohort, 2.0%; breastfeeding cohort, 1.0%.
Unknown or missing: full cohort, 1.7%; breastfeeding cohort, 0.3%.
Unknown or missing: full cohort, 1.7%; breastfeeding cohort, 0.2%.
Unknown or missing: full cohort, 15.0%; breastfeeding cohort, 6.0%.
Unknown or missing: full cohort, 11.9%; breastfeeding cohort, 0.0%.
No delivery in the past year in the postpartum cohort: 70.1%.
Unknown or missing: full cohort, 1.2%; breastfeeding cohort, 0.6%.
At least 1 of the following: abortion, aspiration and curettage, dilation and curettage, excision or biopsy of cervix or uterus, ablation, colposcopy and other cervical procedures, hysteroscopy procedure, laminaria procedure, laparoscopy, lysis adhesions, myomectomy, nerve procedure, salpingectomy, or oophorectomy.
Including need for cervical dilation, ultrasound guidance, paracervical block, use of misoprostol, and clinician indicating difficulty.