Table 1 |
|||||
| Descriptive characteristics of newborns and parents | |||||
|
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 |
The newborns were live singleton births from January 1997 to December 2010 in a perinatal hospital in Hamamatsu, Japan (n = 19,221).
*Sum of medically indicated PTB and spontaneous PTB may not equal PTB less than 37 weeks because of missing data for delivery or induction variables.
†Body mass index was calculated as body weight (kg) divided by height squared (m2).
‡Ex-smoker included mothers who quit smoking during pregnancy.
§Obtained by the chi-square test or analysis of variance.
BMI body mass index; LBW low birth weight; PTB preterm birth, SD standard deviation.
Yorifuji et al. BMC Pregnancy and Childbirth 2012 12:162 doi:10.1186/1471-2393-12-162
