Table 1.
Maternal characteristics and perinatal outcomes by IQ.
| IQ at 4 years | IQ at 7 years | |||||||
|---|---|---|---|---|---|---|---|---|
| Characteristics | IQ ≥90 | IQ <70 | χ2 | P | IQ ≥90 | IQ <70 | χ2 | P |
| N(%) | 18,656 (95.4) | 904 (4.6) | 20,447 (96.3) | 784 (3.7) | ||||
| Maternal age (year) | 90.1 | <0.0001 | 28.5 | <0.0001 | ||||
| <20 | 3,645 (19.5) | 290 (32.1) | 4,076 (19.9) | 212 (27.0) | ||||
| 20–24 | 6,634 (35.6) | 295 (32.6) | 7,528 (36.8) | 242 (30.9) | ||||
| 25–29 | 4,266 (22.9) | 146 (16.2) | 4,569 (22.4) | 159 (20.3) | ||||
| 30–34 | 2,462 (13.2) | 103 (11.4) | 2,555 (12.5) | 107 (13.7) | ||||
| ≥ 35 | 1,649 (8.8) | 70 (7.7) | 1,719 (8.4) | 64 (8.2) | ||||
| Race | 499.9 | <0.0001 | 629.7 | <0.0001 | ||||
| White | 10,763 (57.6) | 180 (19.9) | 12,527 (61.3) | 134 (17.1) | ||||
| Black | 7,305 (39.2) | 666 (73.7) | 7,253 (35.5) | 617 (78.7) | ||||
| Other | 588 (3.2) | 58 (6.4) | 667 (3.3) | 33 (4.2) | ||||
| Parity | 32.7 | <0.0001 | 64.2 | <0.0001 | ||||
| 0 | 5,260 (28.3) | 311 (34.6) | 6,200 (30.4) | 185 (23.7) | ||||
| 1 | 4,412 (23.7) | 146 (16.2) | 4,908 (24.1) | 127 (16.3) | ||||
| ≥ 2 | 8,944 (48.0) | 443 (49.2) | 9,296 (45.6) | 468 (60.0) | ||||
| Social economic status | 584.7 | <0.0001 | 746.0 | <0.0001 | ||||
| 1 (Lowest) | 923 (5.0) | 160 (18.4) | 926 (4.6) | 150 (19.9) | ||||
| 2 | 4,555 (24.8) | 382 (43.7) | 4,623 (23.0) | 363 (48.1) | ||||
| 3 | 5,832 (31.8) | 256 (29.4) | 6,254 (31.1) | 188 (24.9) | ||||
| 4 | 4,505 (24.5) | 60 (6.9) | 5,161 (25.7) | 45 (6.0) | ||||
| 5 (Highest) | 2,552 (13.9) | 14 (1.6) | 3,146 (15.6) | 8 (1.1) | ||||
| Maternal education levels (year) | 350.7 | <0.0001 | 500.3 | <0.0001 | ||||
| Less than high school (≤9) | 4,229 (22.7) | 436 (48.2) | 4,409 (21.6) | 424 (54.1) | ||||
| High school (10–12) | 11,748 (62.9) | 446 (49.6) | 12,655 (61.9) | 352 (44.9) | ||||
| College and above (> 12) | 2,679 (14.4) | 22 (2.4) | 3,383 (16.6) | 8 (1.0) | ||||
| Married | 15,198 (81.5) | 598 (66.2) | 130.1 | <0.0001 | 16,877 (82.5) | 504 (64.3) | 169.5 | <0.0001 |
| Smoking during pregnancy | 8,958 (48.3) | 380 (42.4) | 11.9 | 0.001 | 9,735 (47.9) | 329 (42.4) | 9.0 | 0.003 |
| Maternal BMI (kg/m2) | 3.7 | 0.295 | 27.8 | <0.0001 | ||||
| <18.5 | 2,594 (14.1) | 107 (12.2) | 3,071 (15.2) | 89 (11.9) | ||||
| 18.5–25 | 11,863 (64.4) | 561 (64.2) | 13,038 (64.6) | 455 (60.8) | ||||
| 25–30 | 2,637 (14.3) | 139 (15.9) | 2,728 (13.5) | 126 (16.8) | ||||
| ≥ 30 | 1,331 (7.2) | 67 (7.7) | 1,343 (6.7) | 78 (10.4) | ||||
| Preterm delivary | 76.5 | <0.0001 | 153.2 | <0.0001 | ||||
| Early preterm | 458 (2.4) | 54 (6.0) | 18,192 (89) | 598 (76.3) | ||||
| Late preterm | 1,617 (8.7) | 127 (14.0) | 1,754 (8.6) | 120 (15.3) | ||||
| Term | 16,581 (88.9) | 723 (80.0) | 501 (2.5) | 66 (8.4) | ||||
| Preeclampsia | 425 (2.3) | 32 (3.6) | 6.1 | 0.014 | 463 (2.3) | 30 (3.9) | 8.2 | 0.004 |
| Chronic hypertension | 3,727 (20.0) | 179 (19.9) | 0.0 | 0.931 | 4,083 (20.0) | 172 (22.1) | 1.9 | 0.166 |
| Gestational diabetes | 438 (2.4) | 11 (1.2) | 4.9 | 0.027 | 483 (2.4) | 11 (1.4) | 3.0 | 0.081 |
| Preexisting diabetes | 290 (1.6) | 9 (1.0) | 1.8 | 0.181 | 324 (1.6) | 7 (0.9) | 2.3 | 0.126 |
IQ, intelligence quotient; Early preterm, Gestational age at birth <34 weeks;
Late preterm, Gestational age at birth ≥34 and <37 weeks;
Term, Gestational age at birth ≥37 and ≤ 44 weeks.