Table 1. Characteristics of the cohort by age of menarche.
| Maternal & Obstetric Characteristics |
Menarche aged ≤11y (n=4,521) |
Menarche aged 12y to 14y (n=28,673) |
Menarche aged ≥15y (n=4,875) |
*P= |
|---|---|---|---|---|
| Maternal characteristics | ||||
| Age at first birth | ||||
| Median (IQR) | 28 (25-31) | 28 (25-31) | 29 (26-32) | <0.001 |
| Menarche to birth interval | ||||
| Median (IQR) | 17 (14-20) | 15 (12-18) | 14 (11-16) | <0.001 |
| Height (cm) | ||||
| Median (IQR) | 167 (163-170) | 168 (164-172) | 169 (165-173) | <0.001 |
| Missing | 48 (1.1) | 267 (0.9) | 46 (0.9) | 0.7 |
| Body mass index | ||||
| Median (IQR) | 24.2 (22.0-27.5) |
22.8 (20.9-25.3) |
21.9 (20.3-23.9) |
<0.001 |
| Missing | 127 (2.8) | 637 (2.2) | 104 (2.1) | 0.04 |
| Smoking status | ||||
| Not daily smoker | 3,970 (87.8) | 25,462 (88.8) | 4,401 (90.3) | <0.001 |
| Daily smoker | 511 (11.3) | 2,856 (10.0) | 409 (8.4) | |
| Missing | 40 (0.9) | 355 (1.2) | 65 (1.3) | |
| Marital status | ||||
| Married | 1,603 (35.5) | 9,780 (34.1) | 1,708 (35.0) | <0.001 |
| Cohabiting | 2,606 (57.6) | 17,362 (60.6) | 2,933 (60.2) | |
| Other | 293 (6.5) | 1,440 (5.0) | 222 (4.6) | |
| Missing | 19 (0.4) | 91 (0.3) | 12 (0.2) | |
| Education | ||||
| Less than degree | 1,399 (30.9) | 7,924 (27.6) | 1,238 (25.4) | |
| Degree | 2,782 (61.5) | 18,881 (65.8) | 3,359 (68.9) | <0.001 |
| Missing | 340 (7.5) | 1,868 (6.5) | 278 (5.7) | |
| Income | ||||
| <300,000NOK | 2,879 (63.7) | 17,233 (60.1) | 2,713 (55.7) | <0.001 |
| >300,000 | 1,486 (32.9) | 10,658 (37.2) | 2,034 (41.7) | |
| Missing | 156 (3.5) | 782 (2.7) | 128 (2.6) | |
| Previous miscarriage | ||||
| 1 or more | 594 (15.3) | 3,530 (14.2) | 615 (14.4) | 0.19 |
| Missing | 628 (13.9) | 3,753 (13.1) | 593 (12.2) | 0.045 |
| Infertility | 407 (9.0) | 2,282 (8.0) | 424 (8.7) | 0.02 |
| Diabetes | 84 (1.9) | 360 (1.3) | 58 (1.2) | 0.003 |
| Obstetric characteristics | ||||
| Pre-eclampsia | 235 (5.2) | 1,217 (4.2) | 152 (3.1) | <0.001 |
| Congenital anomaly | 200 (4.4) | 1,354 (4.7) | 207 (4.2) | 0.27 |
| Gestational age at delivery | ||||
| Median (IQR) | 40 (39-41) | 40 (39-41) | 40 (39-41) | 0.9 |
| Onset of labor | ||||
| Spontaneous | 3,723 (82.3) | 24,348 (84.9) | 4,206 (86.3) | <0.001 |
| Mode of delivery | ||||
| Spontaneous vaginal | 3,279 (72.5) | 21,280 (74.2) | 3,713 (76.2) | <0.001 |
| Assisted vaginal | 839 (18.6) | 5,228 (18.2) | 805 (16.5) | |
| Cesarean | 403 (8.9) | 2,165 (7.6) | 357 (7.3) | |
| Birth weight percentile | ||||
| Median (IQR) | 51 (25-77) | 50 (25-75) | 49 (24-74) | 0.02 |
| Missing | 0 (0.0) | 14 (<0.1) | 5 (0.1) | 0.08 |
*
P values from Kruskal-Wallis test or χ2 test, as appropriate
IQR denotes inter-quartile range. NOK denotes Norwegian Krone