Table 2. Mean placental weight according to potential confounders and child/adolescent mental health outcomes.
| Potential Confounders and Mental Health Outcomes | Mean Placental Weight (g) (SD) | |||||
| n (%) | All | n (%) | Male | n (%) | Female | |
| Potential Confounders | ||||||
| Birth weight (g) | 8934 | 4586 | 4348 | |||
| <2500 | 247 (2.8) | 448 (106) | 110 (2.4) | 455 (108) | 137 (3.2) | 443 (105) |
| 2500–4499 | 8370 (93.7) | 644 (121) | 4259 (92.9) | 646 (121) | 4111 (94.5) | 641 (121) |
| ≥4500 | 317 (3.5) | 860 (138) | 217 (4.7) | 837 (139) | 100 (2.3) | 869 (136) |
| pa | .000 | .000 | .000 | |||
| Gestational age at birth (weeks) | 8930 | 4582 | 4348 | |||
| <37 | 363 (4.1) | 524 (163) | 189 (4.1) | 555 (171) | 174 (4.0) | 528 (154) |
| 37–41 | 8226 (92.1) | 650 (129) | 4213 (92) | 655 (130) | 4013 (92.3) | 644 (127) |
| ≥42 | 341 (3.8) | 600 (127) | 180 (3.9) | 663 (124) | 161 (3.7) | 656 (131) |
| pa | .000 | .000 | .000 | |||
| Maternal age (years) | 8934 | 4586 | 4348 | |||
| <20 | 655 (7.3) | 636 (125) | 336 (7.3) | 645 (120) | 319 (7.3) | 626 (129) |
| 20–34 | 7105 (79.5) | 645 (131) | 3635 (79.3) | 651 (133) | 3470 (79.8) | 639 (129) |
| ≥35 | 1174 (13.1) | 654 (142) | 615 (13.4) | 657 (143) | 559 (12.9) | 652 (141) |
| pa | .012 | .381 | .019 | |||
| Maternal education (years) | 7855 | 3999 | 3856 | |||
| <11 | 2377 (30.3) | 651 (138) | 1184 (29.6) | 657 (136) | 1193 (30.9) | 645 (139) |
| ≥11 | 5478 (69.7) | 645 (127) | 2815 (70.4) | 651 (129) | 2663 (69.1) | 640 (125) |
| pa | .089 | .172 | .265 | |||
| Family structure | 8908 | 4570 | 4338 | |||
| Married/cohabiting | 8453 (94.9) | 647 (132) | 4347 (95.1) | 654 (133) | 4106 (94.7) | 641 (131) |
| Single/widowed/divorced | 455 (5.1) | 620 (127) | 223 (4.9) | 614 (123) | 232 (5.3) | 625 (130) |
| pa | .000 | .000 | .069 | |||
| Family social class (by occupation) | 8646 | 4438 | 4208 | |||
| I | ||||||
| Professional | 521 (6.0) | 647 (132) | 265 (6.0) | 647 (142) | 256 (6.1) | 647 (121) |
| Upper white collar | 1723 (20.0) | 648 (127) | 853 (19.2) | 659 (131) | 870 (20.7) | 638 (122) |
| Lower white collar | 3476 (40.2) | 644 (131) | 1802 (40.6) | 651 (130) | 1674 (39.8) | 638 (131) |
| Farmer ≥8 hectares | 348 (4.0) | 666 (146) | 178 (4.0) | 676 (154) | 170 (4.0) | 655 (136) |
| II | ||||||
| Unskilled worker | 2525 (29.2) | 642 (133) | 1319 (29.7) | 645 (131) | 1206 (28.7) | 640 (135) |
| Farmer <8 hectares | 53 (.6) | 672 (178) | 21 (.5) | 731 (202) | 32 (.7) | 633 (151) |
| pa | .025 | .001 | .565 | |||
| Parity | 8895 | 4565 | 4330 | |||
| 0 | 3029 (34.1) | 623 (128) | 1551 (34) | 629 (128) | 1478 (34.1) | 617 (128) |
| 1 | 2969 (33.4) | 653 (132) | 1485 (32.5) | 658 (134) | 1484 (34.3) | 647 (130) |
| 2 | 1604 (18.0) | 660 (134) | 863 (18.9) | 669 (136) | 741 (17.1) | 650 (126) |
| ≥3 | 1293 (14.5) | 666 (132) | 666 (14.6) | 666 (133) | 627 (14.5) | 666 (136) |
| pa | .000 | .000 | .000 | |||
| Pre-pregnancy BMI (kg/m2) | 8708 | 4478 | 4230 | |||
| <20 | 2136 (24.5) | 612 (121) | 1138 (25.4) | 618 (120) | 998 (23.6) | 606 (123) |
| 20–24.99 | 5078 (58.3) | 649 (130) | 2576 (57.5) | 655 (132) | 2502 (59.1) | 643 (127) |
| ≥25 | 1494 (17.2) | 683 (142) | 764 (17.1) | 688 (142) | 730 (17.3) | 677 (141) |
| pa | .000 | .000 | .000 | |||
| Gestational weight gain (kg) | 8262 | 4244 | 4018 | |||
| <11 | 1911 (23.1) | 620 (132) | 909 (21.4) | 623 (137) | 1002 (25.0) | 617 (128) |
| 11–16.99 | 4310 (52.2) | 645 (126) | 2223 (52.4) | 650 (125) | 2087 (51.9) | 640 (126) |
| ≥17 | 2041 (24.7) | 673 (136) | 1112 (26.2) | 679 (136) | 929 (23.1) | 666 (130) |
| pa | .000 | .000 | .000 | |||
| Smoking during pregnancy | 8696 | 4455 | 4241 | |||
| No | 6989 (80.4) | 649 (131) | 3564 (80.0) | 654 (133) | 3425 (80.8) | 644 (130) |
| Yes | 1707 (19.6) | 633 (130) | 891 (20.0) | 638 (131) | 816 (19.2) | 627 (129) |
| pa | .000 | .001 | .001 | |||
| Number of cigarettes (per day) | 939 | 500 | 439 | |||
| <10 cigarettes | 556 (59.2) | 630 (121) | 293 (58.6) | 634 (116) | 263 (59.9) | 626 (127) |
| ≥10 cigarettes | 383 (40.8) | 631 (138) | 207 (41.4) | 641 (138) | 176 (40.1) | 618 (137) |
| pa | .968 | .539 | .544 | |||
| Mental Health Outcomes | ||||||
| 8-y-olds Rutter (teacher report) b | ||||||
| Probable psychiatric disturbance | 8046 | 4097 | 3949 | |||
| Yes | 1139 (14.2) | 651 (138) | 800 (19.5) | 660 (141) | 339 (8.6) | 632 (130) |
| No | 6907 (85.8) | 646 (129) | 3297 (80.5) | 651 (127) | 3610 (91.4) | 642 (129) |
| pa | .245 | .089 | .145 | |||
| Antisocial disorder | 8046 | 4097 | 3949 | |||
| Yes | 724 (9.0) | 659 (142) | 569 (13.9) | 663 (144) | 155 (3.9) | 646 (135) |
| No | 7322 (91.0) | 646 (129) | 3528 (86.1) | 651 (128) | 3794 (96.1) | 641 (129) |
| pa | .010 | .046 | .683 | |||
| Neurotic disorder | 8046 | 4097 | 3949 | |||
| Yes | 328 (4.1) | 641 (133) | 171 (4.2) | 660 (137) | 157 (4.0) | 621 (126) |
| No | 7718 (95.9) | 647 (130) | 3926 (95.8) | 652 (130) | 3792 (96.0) | 642 (130) |
| pa | .419 | .417 | .041 | |||
| Inattention- hyperactivity | 8061 | 4103 | 3958 | |||
| Yes | 755 (9.4) | 650 (138) | 575 (14.0) | 656 (136) | 180 (4.5) | 628 (140) |
| No | 7306 (90.6) | 647 (129) | 3528 (86.0) | 652 (129) | 3778 (95.5) | 642 (129) |
| pa | .568 | .442 | .163 | |||
| Inattentionc | 8069 | 4108 | 3961 | |||
| Yes | 1703 (21.1) | 650 (135) | 1218 (29.6) | 655 (135) | 485 (12.2) | 639 (132) |
| No | 6366 (78.9) | 646 (129) | 2890 (70.4) | 652 (128) | 3476 (87.8) | 642 (129) |
| pa | .281 | .496 | .625 | |||
| Hyperactivityd | 8067 | 4105 | 3962 | |||
| Yes | 573 (7.1) | 654 (137) | 466 (11.4) | 655 (138) | 107 (2.7) | 653 (132) |
| No | 7494 (92.9) | 646 (129) | 3639 (88.6) | 652 (129) | 3855 (97.3) | 641 (130) |
| pa | .159 | .677 | .354 | |||
| 16-y-olds SWAN (parent report) b | ||||||
| Combined ADHD | 6594 | 3275 | 3319 | |||
| Yes | 349 (5.3) | 659 (138) | 231 (7.1) | 668 (144) | 118 (3.6) | 641 (123) |
| No | 6245 (94.7) | 647 (129) | 3044 (92.9) | 652 (128) | 3201 (96.4) | 642 (129) |
| pa | .098 | .076 | .930 | |||
| Inattentione | 6488 | 3227 | 3261 | |||
| Yes | 332 (5.1) | 663 (138) | 230 (7.1) | 666 (140) | 102 (3.1) | 656 (132) |
| No | 6156 (94.9) | 646 (128) | 2997 (92.9) | 652 (127) | 3159 (96.9) | 641 (129) |
| pa | .024 | .110 | .256 | |||
| Hyperactivity-impulsivityf | 6455 | 3206 | 3249 | |||
| Yes | 306 (4.7) | 650 (135) | 197 (6.1) | 660 (135) | 109 (3.4) | 632 (133) |
| No | 6149 (95.3) | 647 (129) | 3009 (93.9) | 652 (129) | 3140 (96.6) | 642 (128) |
| pa | .677 | .402 | .427 | |||
a
for heterogeneity, analysis of variance.
b
assessment of symptoms based on fulfilment of criteria according to the Rutter B2/Strengths and Weaknesses of ADHD symptoms and Normal behavior (SWAN) scale.
c
assessment based on Rutter item number 16.
d
assessment based on sum of Rutter items 1 and 3.
e
SWAN subscale consisting of sum of 9 items.
f
SWAN subscale consisting of sum of 9 items.