Table 1 Descriptive characteristics of newborns and parents
From: Trends of preterm birth and low birth weight in Japan: a one hospital-based study
1997-2000 (n = 5,515) | 2001-2003 (n = 3,927) | 2004-2006 (n = 4,025) | 2007-2010 (n = 5,754) | p value§ | |
|---|---|---|---|---|---|
Newborn outcomes, n (%) | |||||
PTB less than 37 wk | 501 (9.1) | 412 (10.5) | 484 (12.0) | 614 (10.7) | <0.01 |
PTB 34 to 36 wk | 309 (5.6) | 256 (6.5) | 272 (6.8) | 367 (6.4) | 0.10 |
PTB 28 to 33 wk | 148 (2.7) | 124 (3.2) | 140 (3.5) | 181 (3.1) | 0.16 |
PTB 22 to 27 wk | 44 (0.8) | 32 (0.8) | 72 (1.8) | 66 (1.1) | <0.01 |
Medically indicated, less than 37 wk* | 309 (5.6) | 256 (6.5) | 335 (8.3) | 398 (6.9) | <0.01 |
Spontaneous, less than 37 wk* | 184 (3.3) | 150 (3.8) | 141 (3.5) | 212 (3.7) | 0.60 |
LBW | 774 (14.0) | 601 (15.3) | 691 (17.2) | 908 (15.8) | <0.01 |
Term-LBW | 399 (7.2) | 292 (7.4) | 305 (7.6) | 417 (7.2) | 0.91 |
Female sex, n (%) | 2607 (47.3) | 1903 (48.5) | 1909 (47.4) | 2831 (49.2) | 0.22 |
Parental variables | |||||
Maternal age (yr), mean (SD) | 29.6 (4.4) | 30 (4.7) | 30.5 (4.7) | 31.2 (4.9) | <0.01 |
≤24.9, n (%) | 748 (13.6) | 514 (13.1) | 486 (12.1) | 616 (10.7) | <0.01 |
25-34.9, n (%) | 4128 (74.9) | 2870 (73.1) | 2863 (71.1) | 3815 (66.3) | |
≥35, n (%) | 637 (11.6) | 541 (13.8) | 676 (16.8) | 1323 (23.0) | |
Maternal BMI† at pregnancy, mean (SD) | 20.6 (2.8) | 20.6 (3.0) | 20.8 (3.2) | 20.9 (3.3) | <0.01 |
≤18.5, n (%) | 1112 (20.2) | 809 (20.7) | 836 (20.9) | 1165 (20.3) | <0.01 |
18.6-24.9, n (%) | 4021 (73.1) | 2820 (72.0) | 2829 (70.7) | 4056 (70.6) | |
≥25, n (%) | 371 (6.7) | 287 (7.3) | 334 (8.4) | 524 (9.1) | |
Maternal weight gain during pregnancy (kg), mean (SD) | 8.8 (4.0) | 8.8 (4.1) | 9.2 (4.3) | 9.6 (4.1) | <0.01 |
≤4.9 (%) | 700 (14.2) | 538 (15.4) | 543 (14.4) | 573 (10.3) | <0.01 |
5-9.9 (%) | 2352 (47.6) | 1598 (45.8) | 1574 (41.7) | 2361 (42.5) | |
10-14.9 (%) | 1632 (33.0) | 1140 (32.7) | 1380 (36.6) | 2141 (38.5) | |
≥15 (%) | 260 (5.3) | 212 (6.1) | 278 (7.4) | 481 (8.7) | |
Maternal occupation, n (%) | |||||
Professional worker | 408 (7.5) | 337 (8.7) | 325 (8.4) | 505 (10.1) | <0.01 |
Employee | 1175 (21.6) | 905 (23.4) | 1005 (26.0) | 1548 (31.1) | |
Self-employed worker | 65 (1.2) | 46 (1.2) | 39 (1.0) | 45 (0.9) | |
Part-time worker | 155 (2.9) | 177 (4.6) | 136 (3.5) | 213 (4.3) | |
Housewife | 3627 (66.8) | 2407 (62.2) | 2362 (61.1) | 2670 (53.6) | |
Maternal alcohol intake (drinkers), n (%) | 384 (7.1) | 215 (5.6) | 143 (3.6) | 129 (2.3) | <0.01 |
Maternal smoking, n (%) | |||||
Never smoked | 5210 (95.8) | 3648 (94.4) | 3747 (94.5) | 5428 (94.7) | <0.01 |
Ex-smoker‡ | 54 (1.0) | 75 (1.9) | 98 (2.5) | 154 (2.7) | |
Smoker (during pregnancy) | 176 (3.2) | 142 (3.7) | 122 (3.1) | 147 (2.6) | |
Fertility treatment | 597 (10.8) | 391 (10) | 520 (12.9) | 884 (15.4) | <0.01 |
Caesarean section | 1253 (22.7) | 999 (25.4) | 1170 (29.1) | 1648 (28.6) | <0.01 |
Induction | 1637 (30.9) | 1020 (27.4) | 927 (23.7) | 1386 (24.7) | <0.01 |
Parity (%) | |||||
One | 3023 (54.8) | 2233 (56.9) | 2280 (56.6) | 3165 (55.1) | 0.02 |
Two | 1911 (34.7) | 1282 (32.6) | 1372 (34.1) | 1924 (33.5) | |
Three or more | 581 (10.5) | 412 (10.5) | 373 (9.3) | 651 (11.3) | |
Paternal smoking, n (%) | 2696 (51.4) | 1784 (48.2) | 1656 (42.8) | 1960 (35.6) | <0.01 |