Maternal and infant's characteristics in the ALSPAC and Pelotas birth cohort studies
| Variables | ALSPAC 1991/92 | Pelotas 1982 | Pelotas 1993 | Pelotas 2004 | p* | p† |
| n (%) | n (%) | n (%) | n (%) | |||
| Ethnic origin | ||||||
| White | 11737 (97.4) | 4773 (82.1) | 3996 (77.3) | 3030 (73.1) | <0.001 | <0.001 |
| Black/mixed | 314 (2.6) | 1040 (17.9) | 1170 (22.7) | 1117 (26.9) | ||
| Family income (quintils) | ||||||
| 1st (poorest) | 1727 (20.0) | 1159 (19.9) | 1037 (20.1) | 846 (20.4) | 0.001 | – |
| 2nd | 1726 (20.0) | 1166 (20.1) | 1161 (22.5) | 841 (20.3) | ||
| 3rd | 1727 (20.0) | 1166 (20.1) | 922 (17.8) | 802 (19.3) | ||
| 4th | 1726 (20.0) | 1162 (20.0) | 1029 (19.9) | 846 (20.4) | ||
| 5th (better-off) | 1726 (20.0) | 1163 (20.0) | 1019 (19.7) | 812 (19.6) | ||
| Maternal education (achievement) | ||||||
| CSE/none | 2447 (20.2) | – | – | |||
| Vocational | 1198 (9.9) | |||||
| O-level | 4205 (34.6) | |||||
| A-leve/degree | 4290 (35.3) | |||||
| Maternal schooling (y) | ||||||
| 0–4 | 1922 (33.1) | 1441 (27.9) | 639 (15.6) | |||
| 5–8 | 2425 (41.8) | 2392 (46.4) | 1691 (41.2) | |||
| 9–11 | 646 (11.1) | 911 (17.7) | 1362 (33.2) | |||
| ≥12 | 816 (14.1) | 417 (8.1) | 414 (10.1) | |||
| Age (y) | ||||||
| <20 | 653 (4.8) | 908 (15.6) | 910 (17.6) | 792 (19.1) | <0.001 | – |
| 20–34 | 11669 (85.3) | 4339 (74.6) | 3692 (71.5) | 2800 (67.6) | ||
| ≥35 | 1356 (9.9) | 568 (9.8) | 565 (10.9) | 553 (13.3) | ||
| Marital status | ||||||
| With partner | 11327 (97.5) | 5336 (91.8) | 4528 (87.6) | 3468 (83.6) | <0.001 | <0.001 |
| Single mother | 288 (2.5) | 475 (8.2) | 640 (12.4) | 679 (16.4) | ||
| Parity | ||||||
| 0 | 5644 (45.2) | 2299 (39.5) | 1826 (35.3) | 1644 (39.7) | <0.001 | – |
| 1 | 4330 (34.7) | 1642 (28.2) | 1429 (27.7) | 1085 (26.1) | ||
| ≥ 2 | 2502 (20.1) | 1873 (32.2) | 1913 (37.0) | 1417 (34.2) | ||
| Pre-pregnancy body mass index (kg/m2) | ||||||
| <18.5 | 567 (5.0) | 384 (7.9) | 444 (8.9) | 187 (4.9) | <0.001 | – |
| 18.5–24.9 | 8387 (74.4) | 3428 (70.1) | 3459 (68.9) | 2342 (61.5) | ||
| 25.0–29.9 | 1704 (15.1) | 867 (17.7) | 877 (17.5) | 871 (22.9) | ||
| ≥30 | 621 (5.5) | 213 (4.4) | 239 (4.8) | 408 (10.7) | ||
| Ever smoked during pregnancy | ||||||
| No | 8092 (75.9) | 3747 (64.4) | 3453 (66.8) | 3005 (72.5) | <0.001 | <0.001 |
| Yes | 2572 (24.1) | 2069 (35.6) | 1715 (33.2) | 1142 (27.5) | ||
| Urinary infection during pregnancy | ||||||
| No | 8689 (86.1) | NA | 3365 (66.5) | 2598 (62.9) | <0.001 | – |
| Yes | 1403 (13.9) | 1695 (33.5) | 1535 (37.1) | |||
| Hypertension during pregnancy | ||||||
| No | 10658 (89.3) | NA | 4268 (84.3) | 3157 (76.3) | <0.001 | – |
| Yes | 1281 (10.7) | 793 (15.7) | 982 (23.7) | |||
| Hospital admission during pregnancy | ||||||
| No | 9853 (90.4) | NA | 4733 (91.6) | 3694 (89.1) | <0.001 | – |
| Yes | 1044 (9.6) | 434 (8.4) | 453 (10.9) | |||
| Delivery attended by a doctor | ||||||
| Yes | 2008 (17.7) | 3521 (60.6) | 4505 (88.2) | 3674 (89.1) | <0.001 | <0.001 |
| No | 9344 (82.3) | 2289 (39.4) | 603 (11.8) | 447 (10.9) | ||
| Type of delivery | ||||||
| Vaginal | 10330 (89.9) | 4224 (72.6) | 3609 (69.8) | 2291 (55.2) | <0.001 | <0.001 |
| Caesarean section | 1157 (10.1) | 1592 (27.4) | 1559 (30.2) | 1856 (44.8) | ||
| Intra-uterine growth restriction | ||||||
| No | 11958 (88.5) | 3614 (78.7) | 4401 (86.6) | 3427 (82.9) | <0.001 | <0.001 |
| Yes | 1547 (11.5) | 976 (21.3) | 684 (13.4) | 708 (17.1) | ||
| Preterm birth (<37 weeks of gestational age) | ||||||
| No | 12962 (94.8) | 4330 (94.2) | 4535 (89.1) | 3574 (86.4) | <0.001 | <0.001 |
| Yes | 716 (5.2) | 265 (5.8) | 557 (10.9) | 561 (13.6) | ||
| Breast feeding (months) | ||||||
| ≥3 | 4738 (43.5) | 746 (51.5) | 825 (62.7) | 2860 (74.7) | <0.001 | <0.001 |
| <3 | 6149 (56.5) | 703 (48.5) | 492 (37.3) | 967 (25.3) | ||