TABLE 1.
Study Demographic Variables and Other Covariates for the Miscarriage Analysis
| Characteristic | Flight Attendants | Teachers |
|---|---|---|
| Study women; no.a | 673 | 91 |
| Demographic variables | ||
| Age at interview (years); median (range) | 38 (26–19) | 37 (29–49) |
| Nonwhite race; no. (%) | 47 (7) | 15 (16) |
| Hispanic ethnicity; no. (%) | 48 (7) | 3 (3) |
| Body mass index at interview (kg/m2); median (range) | 21 (17–38) | 23 (17–45) |
| Education; no. (%) | ||
| No collegeb | 89 (13) | 0 (0) |
| Some college | 292 (43) | 1 (1) |
| College graduate or higher | 292 (43) | 90 (99) |
| Annual family income; no. (%) | ||
| Unknown | 13 | 0 |
| <$50,000 | 92 (14) | 21 (23) |
| $50,000–$74,999 | 166 (25) | 26 (29) |
| $75,000 or higher | 402 (61) | 44 (48) |
| Study pregnancies; no.c | 840 | 118 |
| Time from end of pregnancy to interview (years); median (range) | 5.5 (3.0–8.1) | 5.6 (3.4–8.0) |
| Reproductive factors during pregnancy | ||
| Age at last menstrual period (years); median (range) | 32 (20–43) | 31 (24–42) |
| Gravidity (no. previous pregnancies); no. (%) | ||
| Unknown | 30 | 0 |
| 0 | 298 (37) | 49 (42) |
| 1 | 272 (34) | 28 (24) |
| 2+ | 240 (30) | 41 (35) |
| Parity (no. previous live births); no. (%) | ||
| Unknown | 16 | 0 |
| No prior pregnancies | 298 | 49 |
| 0 | 199 (38) | 20 (29) |
| 1 | 243 (46) | 39 (57) |
| 2+ | 84 (16) | 10 (14) |
| No. previous miscarriages; no. (%) | ||
| Unknown | 23 | 0 |
| No prior pregnancies | 298 | 49 |
| 0 | 312 (60) | 37 (54) |
| 1 | 160 (31) | 25 (36) |
| 2+ | 47 (9) | 7 (10) |
| Years since last pregnancy; median (range) | 1.8 (0–19) | 1.9 (0.3–14) |
| Occupational factors during pregnancy | ||
| Job tenure at last menstrual period (years); median (range)d | 6.3 (0.1–23) | NA |
| Exposed to coworkers’, customers’, or clients’ smoke in pregnancy | 152 (18) | 4 (3) |
| Low job control at work in pregnancye | 216 (26) | 18 (15) |
| Low supervisor support in pregnancyf | 651 (79) | 61 (53) |
| Somewhat hard or very hard physical effort at work in pregnancy | 441 (53) | 19 (16) |
| High physical job demands in pregnancyg | 665 (80) | 24 (21) |
| Lifting/carrying at least 15 pounds more than 10 times/day at work in pregnancy | 433 (52) | 12 (10) |
| Being on feet more than 8 hours/day at work in pregnancy | 474 (57) | 16 (14) |
| Bending at the waist more than 25 times/day at work in pregnancy | 675 (82) | 44 (38) |
| Pushing/pulling at least 15 pounds 20 or more times/day at work in pregnancy | 521 (63) | 8 (7) |
| Husband's occupation; no. (%) | ||
| Reproductive hazard exposure possibleh | 159 (20) | 19 (17) |
| Reproductive hazard exposure not likely | 485 (61) | 91 (83) |
| Flight crew | 148 (19) | 0 (0) |
| Lifestyle factors during pregnancy | ||
| Smoked during first trimester | 31 (4) | 3 (3) |
| Lived with a smoker during pregnancy | 47 (6) | 10 (8) |
| Smoked or lived with a smoker during pregnancy | 71 (9) | 11 (9) |
| Caffeine use in first trimesteri | ||
| None | 320 (39) | 54 (46) |
| Low | 330 (40) | 41 (35) |
| High | 179 (22) | 23 (19) |
| Alcohol use in first trimester | 208 (25) | 26 (22) |
| Home stress in pregnancyj | 230 (28) | 34 (29) |
| Any children at home under age 4 years in pregnancy | 278 (34) | 36 (31) |
| Any use of very hot baths or hot tubs/sauna in pregnancy | 199 (24) | 38 (32) |
| High use (>4/month) of very hot baths or hot tubs/sauna in pregnancy | 69 (8) | 14 (12) |
| High vigorous physical activity (>120 minutes/week) in pregnancy | 271 (33) | 32 (27) |
| Medical factors during pregnancy | ||
| Bladder, kidney, urinary tract infection in first trimester | 20 (2) | 1 (1) |
| Illness with fever in first trimester | 13 (2) | 1 (1) |
| Injury in first trimesterk | 8 (1) | 0 (0) |
| Selected injury in first trimesterl | 7 (1) | 0 (0) |
| X-rays or radiotherapy during first trimester or in 3 months before pregnancy | 17 (2) | 2 (2) |
| Thyroid condition prior to pregnancy or during first trimester | 16 (2) | 2 (2) |
| Benign tumor of the reproductive organs before or during pregnancy | 52 (6) | 7 (6) |
| Pelvic inflammatory disease before or during pregnancy | 23 (3) | 0 (0) |
| Chlamydia before or during pregnancy | 36 (4) | 5 (4) |
| Herpes, human papillomavirus, gonorrhea before or during pregnancy | 46 (6) | 7 (6) |
| Cervical procedures before or during pregnancy | 89 (11) | 5 (4) |
| Fibroid procedures before or during pregnancy | 15 (2) | 1 (1) |
Due to missing values, sample size varies (660–673 for flight attendants; 90–91 for teachers).
Percentages may not sum to 100 due to rounding.
Summary statistics assume independence among the study pregnancies and are not adjusted for other variables. Due to missing values, sample size varies (792–840 for flight attendant pregnancies; 110–118 for teacher pregnancies).
Job tenure at last menstrual period is based on company-provided hire dates for flight attendant pregnancies and not available for teacher pregnancies.
Low job control defined as “your job allowed you to make a lot of decisions on your own”: never, seldom, or sometimes.
Low supervisor support defined as “management was concerned about the welfare of employees”: never, seldom, or sometimes.
High physical job demands defined as (1) being on your feet (including standing and walking) more than 8 hours/day or (2) 2 or more of the following: lifting or carrying objects that weigh at least 15 pounds more than 10 times a day, bending at the waist more than 25 times/day, and pushing or pulling heavy objects requiring at least 15 pounds of force or effort 20 or more times/day.
Job title, business, and main duties data for husbands during the pregnancy were categorized by expert judgment and consultation with National Institute for Occupational Safety and Health industrial hygienists, based on understanding of reproductive hazards in a variety of workplaces.
Caffeine use defined as any consumption of caffeinated coffee, tea, or soft drinks during the relevant time period. High caffeine use defined as daily caffeine consumption exceeding 85 mg computed from the usual number of drinks/day of caffeinated coffee (~85 mg/drink), tea (~40 mg/drink), and soft drinks (~36 mg/drink) during the relevant time period.
Home stress during pregnancy defined as 2 or more of the following: (1) responsibilities at home were shared with others never, seldom, or sometimes, (2) exposed to hostility or conflict at home sometimes, often, or all the time, and (3) having a close friend or family member with whom I could talk about my true feelings when I needed to never, seldom, or sometimes; or 1 or more of the following: (1) responsibilities at home were shared with others never or seldom, (2) exposed to hostility or conflict at home sometimes, often, or all the time, or (3) having a close friend or family member with whom I could talk about my true feelings when I needed to never or seldom.
Includes all injuries reported for the question “during this pregnancy, did you have any serious injury or an accident with injury that required a visit to a doctor?”
Limited to self-reported falls, auto accidents, or shock reported for the question “during this pregnancy, did you have any serious injury or an accident with injury that required a visit to a doctor?”
NA indicates not available.