Table 1.
Age-standardized characteristics of the study population by first-trimester work schedule
| First-trimester work schedule | |||
|---|---|---|---|
| Days only (n = 4494, 68%) | Evenings or rotating shifts without nights (n = 1120, 17%) | Fixed or rotating nights (n = 996, 15%) |
|
| Maternal age at index pregnancy, mean (SD) | 36.6 (3.4) | 35.9 (3.3) | 35.9 (3.4) |
| Hispanic or non-White, % | 4 | 3 | 5 |
| Region, % | |||
| Northeast | 32 | 39 | 33 |
| Midwest | 35 | 37 | 36 |
| South | 19 | 12 | 17 |
| West | 14 | 11 | 14 |
| Pre-pregnancy BMI (kg/m2), % | |||
| <25 | 71 | 71 | 66 |
| 25–29 | 19 | 19 | 23 |
| ≥30 | 10 | 9 | 11 |
| Pre-pregnancy physical activity (MET-h/week), % | |||
| <9 | 36 | 35 | 37 |
| 9–26 | 35 | 36 | 34 |
| ≥27 | 29 | 29 | 29 |
| Pre-pregnancy SES scorea | 0.70 (4.61) | 0.97 (4.11) | 0.18 (4.67) |
| Husband’s level of education, % | |||
| High school or less | 15 | 15 | 18 |
| College (2 or 4 years) | 50 | 53 | 52 |
| Graduate school | 29 | 28 | 25 |
| Other/missing | 5 | 4 | 5 |
| First-trimester caffeinated coffee intake (1 cup = 8 oz), % | |||
| None or <1 cup/week | 63 | 62 | 60 |
| 1 cup/week–1 cup/day | 28 | 29 | 27 |
| ≥2 cups/day | 10 | 9 | 13 |
| First-trimester caffeinated soda or tea intake (1 serving = 12 oz soda, 8 oz tea or 16 oz iced tea), % | |||
| None or <1 serving/week | 49 | 50 | 43 |
| 1 serving/week–1 serving/day | 40 | 42 | 44 |
| ≥2 servings/day | 11 | 9 | 13 |
| First-trimester alcohol intake (1 drink = 12 oz beer, 6 oz wine, or 1 oz liquor), % | |||
| None | 81 | 82 | 84 |
| <1 drink/week | 14 | 14 | 13 |
| ≥1 drinks/week | 5 | 4 | 3 |
| First-trimester smoked cigarettes, % | 6 | 5 | 6 |
| Work setting,b % | |||
| Acute care setting | 24 | 36 | 48 |
| Non-acute care setting | 44 | 35 | 24 |
| Other/missing | 32 | 29 | 28 |
| Parous at index pregnancy, % | 84 | 90 | 88 |
| Prior gestational hypertension,c % | 11 | 11 | 10 |
| Prior preeclampsia,c % | 7 | 7 | 7 |
| Morning preference chronotype, % | 64 | 51 | 46 |
| First-trimester hours worked per week, % | |||
| 1–20 | 21 | 46 | 22 |
| 21–40 | 59 | 49 | 64 |
| ≥41 | 20 | 6 | 13 |
| First-trimester hours spent standing per day at work, % | |||
| 0–4 | 40 | 16 | 11 |
| 5–8 | 44 | 63 | 47 |
| ≥9 | 17 | 21 | 42 |
| First-trimester number of times heavy lifting per day at work,d % | |||
| None | 45 | 22 | 20 |
| 1–5 | 38 | 48 | 42 |
| ≥6 | 17 | 30 | 38 |
Values are means (SD) for continuous variables, percentages for categorical variables and are standardized to the age distribution of the study population (except maternal age at index pregnancy).
aSES is based on the sum of the z-scores of census tract indicators based on participants’ zip codes (median household income, home value, percentage with college degree, percentage of families with interest or dividends, percentage occupied housing, percentage living in poverty, percentage White).
bAcute care settings include critical care, emergency room, operating room; non-acute care settings include medical/surgical floor, general paediatrics, rehabilitation, home/community, education/research or administration.
cPer cent of patients calculated from among parous participants only (nulliparous women excluded).
dLifting refers to lifting or moving a physical load of 25 pounds or more, including repositioning or transferring patients.