Table 1.
Characteristics of the study population recruited from three US cities during 2000-4
| Population characteristics | PTD | SGAa | Birth weight (g) | |||
|---|---|---|---|---|---|---|
| n | % | % | % | Mean | SD | |
| Total population | 2039 | 100 | 9 | 5 | 3382 | 586 |
| Maternal race/ethnicity | ||||||
| Non-Hispanic white | 1169 | 57 | 7 | 5 | 3486 | 596 |
| Non-Hispanic black | 609 | 30 | 12 | 7 | 3167 | 545 |
| Hispanic | 185 | 9 | 9 | 6 | 3427 | 632 |
| Other | 73 | 4 | 7 | -- | 3400 | 459 |
| Missing | 3 | |||||
| Maternal age (years) | ||||||
| < 25 | 599 | 29 | 11 | 7 | 3255 | 558 |
| 25-29 | 657 | 32 | 8 | 6 | 3393 | 572 |
| 30-34 | 564 | 28 | 7 | 4 | 3486 | 587 |
| ≥35 | 219 | 11 | 11 | 6 | 3425 | 642 |
| Highest maternal education level | ||||||
| High school or less | 573 | 28 | 13 | 9 | 3235 | 616 |
| Some college | 440 | 22 | 10 | 5 | 3340 | 600 |
| College degree or higher | 1025 | 50 | 7 | 4 | 3482 | 544 |
| Maternal smoking | ||||||
| Yes | 99 | 5 | 16 | 12 | 3073 | 578 |
| No | 1940 | 95 | 9 | 5 | 3398 | 583 |
| Maternal alcohol use | ||||||
| Yes | 32 | 2 | 9 | 6 | 3410 | 702 |
| No | 2007 | 98 | 6 | 6 | 3381 | 585 |
| Pre-pregnancy BMI (kg/m2) | ||||||
| < 19.8 | 232 | 11 | 8 | 9 | 3291 | 535 |
| 19.8-25.9 | 1016 | 50 | 8 | 5 | 3410 | 553 |
| 26.0-29.9 | 333 | 16 | 7 | 6 | 3421 | 535 |
| > 29.9 | 407 | 20 | 14 | 5 | 3349 | 713 |
| Missing | 51 | 3 | 10 | 16 | 3255 | 771 |
| Vitamin use | ||||||
| Yes | 1027 | 50 | 7 | 5 | 3461 | 573 |
| No | 1012 | 50 | 11 | 7 | 3302 | 590 |
| Caffeine intake (mg/day) | ||||||
| None | 519 | 25 | 9 | 4 | 3410 | 613 |
| 1-150 | 468 | 23 | 8 | 5 | 3385 | 557 |
| 151-300 | 387 | 19 | 11 | 6 | 3344 | 617 |
| > 300 | 665 | 33 | 9 | 7 | 3380 | 567 |
| Marital status | ||||||
| Married | 1390 | 68 | 7 | 5 | 3466 | 536 |
| Not married | 648 | 32 | 13 | 8 | 3200 | 646 |
| Missing | 1 | |||||
| Parity | ||||||
| Nulliparous | 991 | 49 | 10 | 6 | 3323 | 591 |
| Parous | 1048 | 51 | 8 | 4 | 3438 | 577 |
| Employed during past 4 months | ||||||
| Yes | 1430 | 70 | 9 | 5 | 3372 | 580 |
| No | 608 | 30 | 9 | 7 | 3406 | 602 |
| Annual household income ($) | ||||||
| < 30,000 | 637 | 31 | 12 | 7 | 3245 | 629 |
| 30,001-60,000 | 535 | 26 | 7 | 7 | 3437 | 545 |
| 60,001-80,000 | 321 | 16 | 6 | 5 | 3460 | 498 |
| > 80,000 | 465 | 23 | 8 | 3 | 3504 | 571 |
| Missing | 81 | 4 | 20 | 10 | 3078 | 614 |
| Recreational activityb | ||||||
| Yes | 1109 | 54 | 9 | 6 | 3423 | 572 |
| No | 930 | 46 | 10 | 5 | 3332 | 600 |
| Vigorous recreational activityc | ||||||
| Yes | 401 | 20 | 8 | 7 | 3412 | 559 |
| No | 1638 | 80 | 9 | 5 | 3374 | 593 |
| Swimming | ||||||
| Yes | 651 | 58 | 6 | 6 | 3471 | 549 |
| No | 1388 | 32 | 10 | 6 | 3340 | 599 |
| Infant gender | ||||||
| Male | 1045 | 51 | 9 | 7 | 3419 | 585 |
| Female | 994 | 49 | 9 | 5 | 3343 | 586 |
| Study site | ||||||
| Site 1 | 929 | 46 | 6 | 5 | 3459 | 581 |
| Site 2 | 761 | 37 | 11 | 6 | 3329 | 593 |
| Site 3 | 349 | 17 | 13 | 8 | 3294 | 562 |
aTerm births only
bAny recreational physical activity or exercise, such as brisk walking, jogging, swimming, biking, tennis, soccer, or dancing
cAny recreational physical activity or exercise, such as brisk walking, jogging, swimming, biking, tennis, soccer, or dancing that caused large increases in breathing and heart rate
SGA = small for gestational age; PTD = preterm delivery; SD = standard deviation; BMI = body mass index