Table 1.
Maternal and infant characteristics by maternal age category among 30,831. Japanese women under 25 years of age.
| Mean (SD) or n (%) | Maternal age | pa | ||
|---|---|---|---|---|
| Junior adolescent (n = 122) | Senior adolescent (n = 3,863) | Young adult (n = 26,846) | ||
| Maternal characteristics | ||||
| Maternal age at birth (years) | 14.7 (0.6) | 18.2 (1.0) | 22.5 (1.3) | <0.001 |
| Pre-pregnancy weight (kg) | 48.6 (7.4) | 50.5 (8.2) | 51.5 (9.0) | <0.001 |
| Maternal height (cm) | 155.5 (5.6) | 156.5 (5.4) | 157.4 (5.5) | <0.001 |
| Pre-pregnancy body mass index (kg/m2) | 20.1 (2.5) | 20.6 (3.1) | 20.8 (3.4) | 0.001 |
| Weight gain during pregnancy (kg) | 11.2 (5.0) | 11.1 (5.0) | 10.8 (4.9) | <0.001 |
| Multipara (%) | 1 (0.8) | 411 (10.6) | 8,004 (29.8) | <0.001 |
| Pre-existing hypertension (%) | 0 (0.0) | 3 (0.1) | 65 (0.2) | 0.110 |
| Pre-existing diabetes or gestational diabetes (%) | 0 (0.0) | 41 (1.1) | 407 (1.5) | 0.035 |
| Smoking | <0.001 | |||
| Yes | 15 (12.3) | 465 (12.0) | 2,162 (8.1) | |
| No | 82 (67.2) | 2,196 (56.9) | 16,627 (61.9) | |
| Unanswered | 25 (20.5) | 1,202 (31.1) | 8,057 (30.0) | |
| Birth outcomes | ||||
| Birthweight (g) | 2891 (584) | 2838 (577) | 2856 (561) | 0.152 |
| Gestational age at birth (weeks) | 38.3 (2.7) | 38.3 (2.8) | 38.3 (2.6) | 0.792 |
| Infant sex male (%) | 70 (57.4) | 2,006 (51.9) | 13,700 (51.0) | 0.226 |
| Pregnancy complications | ||||
| Cesarean section (%) | 21 (17.2) | 630 (16.3) | 5,549 (20.7) | <0.001 |
| Unplanned cesarean section (%) | 18 (14.8) | 444 (11.5) | 3,228 (12.0) | 0.406 |
| Preeclampsia (%) | 4 (3.3) | 99 (2.6) | 705 (2.6) | 0.878 |
| Severe preeclampsia (%) | 1 (0.8) | 45 (1.2) | 296 (1.1) | 0.899 |
| Preterm birth (%) | 18 (14.8) | 545 (14.1) | 3,487 (13.0) | 0.136 |
| Very preterm birth (%) | 4 (3.3) | 147 (3.8) | 865 (3.2) | 0.165 |
| Extremely preterm birth (%) | 2 (1.6) | 59 (1.5) | 317 (1.2) | 0.172 |
| Low birth weight | 24 (19.7) | 763 (19.8) | 5,034 (18.8) | 0.324 |
| Low Apgar at 5 minute (%) | 5 (4.1) | 107 (2.8) | 551 (2.1) | 0.005 |
| Low pH of umbilical cord artery (%) | 3 (2.5) | 38 (1.0) | 203 (0.8) | 0.038 |
| Severe lacerationb (%) | 3 (3.0) | 49 (1.5) | 307 (1.4) | 0.326 |
| Stillbirth/early neonatal death (%) | 0 (0.0) | 28 (0.7) | 184 (0.7) | 0.630 |
Junior adolescent: Women aged ≤16.
Senior adolescent: Women aged 16–19.
Young adult: Women aged 20–24.
ap value using chi-square test for categorical variables and one-way ANOVA test for continuous variables.
bAnalysis for this cell is n = 24,631 (excluded women who received cesarean-section).