Table 1 Maternal and infant characteristics by maternal age category among 365,417 Japanese women
Mean (SD) or n (%) | Maternal age | |||
|---|---|---|---|---|
30–34 (n = 204,181) | 35–39 (n = 131,515) | 40–44 (n = 28,797) | ≥45 (n = 924) | |
Maternal characteristics | ||||
 Pre-pregnancy weight (kg) | 52.9 (7.4) | 54.0 (7.8) | 54.8 (8.0) | 55.0 (8.4) |
 Height (cm) | 158.4 (4.5) | 158.5 (4.6) | 158.4 (4.7) | 157.9 (4.5) |
 Pre-pregnancy BMI (kg/m2) | 21.1 (2.8) | 21.5 (3.0) | 21.8 (3.1) | 22.1 (3.2) |
 Weight gain during pregnancy (kg) | 9.4 (3.5) | 9.0 (3.6) | 8.8 (3.7) | 8.7 (3.9) |
 Primipara | 99,359 (48.7) | 55,296 (42.0) | 12,788 (44.4) | 448 (48.5) |
 Preexisting hypertension | 1241 (0.6) | 1576 (1.2) | 545 (2.0) | 32 (3.5) |
 Preexisting diabetes or GDM | 5184 (2.5) | 5009 (3.8) | 1520 (5.3) | 79 (8.5) |
 Assisted conception | 4963 (2.4) | 8641 (6.6) | 3987 (13.8) | 201 (21.8) |
 Smoking during pregnancy | 11,299 (5.5) | 6866 (5.2) | 1549 (5.4) | 77 (8.3) |
Birth outcomes | ||||
 Birthweight (g) | 2881 (554) | 2877 (568) | 2861 (588) | 2848 (607) |
 Gestational age at birth (w) | 38.2 (2.5) | 38.0 (2.5) | 37.9 (2.5) | 37.7 (2.5) |
 Infant sex male | 105,286 (51.6) | 67,695 (51.5) | 14,797 (51.4) | 478 (51.7) |
Pregnancy complications | ||||
 Cesarean section | 57,881 (28.3) | 46,252 (35.2) | 12,516 (43.5) | 506 (54.8) |
 Emergency cesarean section | 26,812 (13.1) | 19,922 (15.1) | 5452 (18.9) | 215 (23.3) |
 Preeclampsia | 5304 (2.6) | 4192 (3.2) | 1140 (4.0) | 53 (5.7) |
 Severe preeclampsia | 1832 (0.9) | 1446 (1.1) | 388 (1.3) | 20 (2.2) |
 Placenta previa | 3485 (1.7) | 3081 (2.3) | 805 (2.8) | 40 (4.3) |
 Placental abruption | 1908 (0.9) | 1338 (1.0) | 286 (1.0) | 12 (1.3) |
 Preterm birth | 25,754 (12.6) | 17,647 (13.4) | 4171 (14.5) | 155 (16.8) |
 Very preterm birth | 6111 (3.0) | 4178 (3.2) | 952 (3.3) | 29 (3.1) |
 Extremely preterm birth | 2195 (1.1) | 1434 (1.1) | 287 (1.0) | 8 (0.9) |
 Low birthweight | 36,462 (17.9) | 23,793 (18.1) | 5563 (19.3) | 201 (21.8) |
 Small for gestational age | 9067 (4.4) | 5846 (4.4) | 1449 (5.0) | 52 (5.6) |
 Low apgar at 5 min | 4373 (2.1) | 2945 (2.2) | 690 (2.4) | 22 (2.4) |
 Low pH of umbilical cord artery | 1563 (0.8) | 1116 (0.8) | 2820 (1.0) | 10 (10.8) |
 Perinatal death | 1473 (0.7) | 924 (0.7) | 224 (0.8) | 11 (1.2) |