Table I.
Descriptive characteristics of the study population according to parental time to pregnancy and use of medically assisted reproduction (MAR) among 13 285 mother–child dyads in the Puberty Cohort, Denmark, 2012–2018.
| Time to pregnancy (TTP) in months (mo) and use of MAR | |||||||
|---|---|---|---|---|---|---|---|
| TTP: ≤5 mo | TTP: 6–12 mo | TTP: >12 mo | TTP: 6–12 mo + MAR | TTP: >12 mo + MAR | Total | Missing/n (%) | |
| N (%) | 8541 (64.3) | 2038 (15.3) | 1242 (9.3) | 230 (1.7) | 1234 (9.3) | 13285 (100.0) | |
| Covariates | |||||||
| Sex, n (%) | 0/13 285 (0) | ||||||
| Boys | 4138 (48.4) | 1016 (49.9) | 595 (47.9) | 113 (49.1) | 606 (49.1) | 6468 (48.7) | |
| Girls | 4403 (51.6) | 1022 (50.1) | 647 (52.1) | 117 (50.9) | 628 (50.9) | 6817 (51.3) | |
| Gestational age, n (%) | 60/13 285 (0.5) | ||||||
| ≥37 weeks | 7923 (93.2) | 1870 (92.1) | 1136 (91.8) | 213 (94.7) | 1134 (92.3) | 12276 (92.8) | |
| <37 weeks | 580 (6.8) | 161 (7.9) | 101 (8.2) | 12 (5.3) | 95 (7.7) | 949 (7.2) | |
| Birthweight (g), mean (SD) | 3551 (586) | 3518 (603) | 3497 (606) | 3524 (542) | 3465 (615) | 3532 (593) | 49/13 285 (0.4) |
| Parity, n (%) | 0/13 285 (0) | ||||||
| First child | 3993 (46.8) | 1071 (52.6) | 670 (53.9) | 125 (54.3) | 934 (75.7) | 6793 (51.1) | |
| Second or more child | 4548 (53.2) | 967 (47.4) | 572 (46.1) | 105 (45.7) | 300 (24.3) | 6492 (48.9) | |
| Highest social class of parents, n (%) | 29/13 285 (0.2) | ||||||
| High grade professional | 2118 (24.9) | 480 (23.6) | 264 (21.3) | 53 (23.0) | 334 (27.1) | 3249 (24.5) | |
| Low grade professional | 3101 (36.4) | 697 (34.3) | 390 (31.4) | 82 (35.7) | 443 (36.0) | 4713 (35.6) | |
| Skilled worker | 2235 (26.2) | 569 (28.0) | 391 (31.5) | 74 (32.2) | 316 (25.7) | 3585 (27.0) | |
| Unskilled worker | 1064 (12.5) | 289 (14.2) | 197 (15.9) | 21 (9.1) | 138 (11.2) | 1709 (12.9) | |
| Maternal age (years), mean (SD) | 30.3 (4.0) | 30.5 (4.2) | 31.7 (4.5) | 31.8 (4.8) | 32.2 (4.1) | 30.6 (4.1) | 3/13 285 (0.1) |
| Maternal age of menarche, n (%)a | 105/13 285 (0.8) | ||||||
| Earlier than peers | 2147 (25.4) | 481 (23.8) | 309 (25.0) | 54 (23.7) | 331 (27.0) | 3322 (25.2) | |
| Same time as peers | 4902 (57.9) | 1179 (58.3) | 694 (56.2) | 126 (55.3) | 663 (54.0) | 7564 (57.4) | |
| Later than peers | 1420 (16.8) | 362 (17.9) | 231 (18.7) | 48 (21.1) | 233 (19.0) | 2294 (17.4) | |
| Pre-pregnancy BMI (kg/m2), n (%) | 168/13 285 (1.3) | ||||||
| <18.5 | 563 (6.7) | 158 (7.8) | 75 (6.1) | 7 (3.1) | 59 (4.8) | 862 (6.6) | |
| ≥18.5 to <25 | 5377 (63.8) | 1208 (60.0) | 664 (54.0) | 146 (64.0) | 713 (58.5) | 8108 (61.8) | |
| ≥25 to <30 | 1741 (20.7) | 428 (21.2) | 303 (24.6) | 47 (20.6) | 281 (23.1) | 2800 (21.3) | |
| ≥30 | 745 (8.8) | 221 (11.0) | 188 (15.3) | 28 (12.3) | 165 (13.5) | 1347 (10.3) | |
| Daily number of cigarettes in first trimester, n (%) | 45/13 285 (0.3) | ||||||
| Non-smoker | 6414 (75.4) | 1460 (71.9) | 825 (66.6) | 187 (81.7) | 999 (81.0) | 9885 (74.7) | |
| 1–10 | 1725 (20.3) | 440 (21.7) | 312 (25.2) | 38 (16.6) | 202 (16.4) | 2717 (20.5) | |
| >10 | 367 (4.3) | 132 (6.5) | 102 (8.2) | 4 (1.7) | 33 (2.7) | 638 (4.8) | |
aFirst, maternal age at menarche (AAM) was reported by the mothers in years. If unable to specify in years, then they were asked to report at which grade or, lastly, whether AAM was experienced earlier, same time or later than peers. Observations with information in years or grade were re-categorized as earlier, same time or later than peers according to national values from the Danish Ministry of Education: earlier than peers; AAM at age of (below or equal to-sign) 12 years or before seventh grade, same as peers; AAM at 13–14 years of during seventh grade, and later than peers; AAM at (equal to or above-sign) 15 years or after seventh grade.