Table 1.
Distributions of carboxyhemoglobin (%) according to pregnancy characteristics within preeclampsia cases and controls.
| Preeclampsia cases (N=128) | Controls (N=419) | |||
|---|---|---|---|---|
| Characteristic | No. (%) | Median (IQR)a | No. (%) | Median (IQR)a |
| Overall | 128 (100.0) | 0.85 (0.74–1.07) | 419 (100.0) | 0.82 (0.70–1.00) |
| Age (years) | ||||
| ≤ 20 | 3 (2.3) | 0.82 (0.67–1.11) | 6 (1.4) | 0.88 (0.86–1.23) |
| 21–34 | 79 (61.7) | 0.87 (0.74–1.17) | 284 (37.8) | 0.82 (0.69–1.00)c |
| 35–39 | 36 (28.1) | 0.82 (0.73–0.98) | 99 (23.6) | 0.84 (0.74–1.02) |
| ≥ 40 | 10 (7.8) | 0.87 (0.72–1.10) | 30 (7.2) | 0.81 (0.67–0.99) |
| Parity | ||||
| Nulliparous | 87 (68.0) | 0.85 (0.74–1.04) | 261 (62.3) | 0.88 (0.75–1.07) |
| Parous | 41 (32.0) | 0.86 (0.74–1.07) | 158 (37.7) | 0.77 (0.66–0.88)c |
| Pre-pregnancy body mass index (kg/m2)b | ||||
| < 18.5 | 7 (5.5) | 0.74 (0.66–0.80) | 21 (5.0) | 0.84 (0.68–1.05) |
| 18.5–24.9 | 51 (39.8) | 0.85 (0.71–1.12) | 290 (69.5) | 0.83 (0.71–1.01) |
| 25–29.9 | 33 (25.8) | 0.87 (0.80–1.04) | 68 (16.3) | 0.81 (0.69–0.98)c |
| ≥ 30 | 37 (28.9) | 0.85 (0.73–1.17) | 38 (9.1) | 0.81 (0.67–1.08) |
| Race/ethnicityb | ||||
| Non–Hispanic white | 107 (84.3) | 0.85 (0.74–1.12) | 357 (85.4) | 0.82 (0.70–1.00) |
| Non–Hispanic black | 5 (3.9) | 1.11 (0.84–1.22) | 9 (2.2) | 0.90 (0.79–1.13) |
| Hispanic | 3 (2.4) | 1.01 (0.70–1.08) | 11 (2.6) | 0.94 (0.81–1.15) |
| Asian/Pacific Islander | 6 (4.7) | 0.83 (0.74–0.90) | 32 (7.7) | 0.81 (0.70–1.02) |
| Other | 6 (4.7) | 0.86 (0.82–0.98) | 9 (2.1) | 0.82 (0.75–1.03) |
| Education | ||||
| ≤ 12 years | 11 (8.6) | 1.11 (0.82–1.18) | 13( 3.1) | 0.86 (0.72–0.95) |
| > 12 years | 117 (91.4) | 0.85 (0.74–1.04) | 406 (96.9) | 0.82 (0.70–1.00) |
| Employed in early pregnancyb | ||||
| Yes | 108 (85.7) | 0.86 (0.74–1.07) | 345 (82.7) | 0.85 (0.72–1.02) |
| No | 18 (14.3) | 0.82 (0.75–1.06) | 72 (17.3) | 0.77 (0.64–0.86)c |
| Marital status | ||||
| Married | 112 (87.5) | 0.84 (0.74–1.05) | 387 (92.4) | 0.82 (0.70–1.00) |
| Unmarried | 16 (12.5) | 0.94 (0.75–1.21) | 32 (7.6) | 0.90 (0.76–1.24) |
| Annual household incomeb | ||||
| < $30,000 | 6 (4.8) | 0.83 (0.67–1.55) | 10 (2.4) | 0.87 (0.71–1.24) |
| $31,000–69,999 | 28 (22.4) | 0.88 (0.67–1.18) | 95 (23.0) | 0.85 (0.72–1.00) |
| ≥ $70,000 | 87 (69.6) | 0.86 (0.73–1.04) | 299 (72.2) | 0.82 (0.70–1.01) |
| Refused | 4 (3.2) | 0.82 (0.74–1.35) | 10 (2.4) | 0.84 (0.63–0.87) |
| Smoking statusb | ||||
| Never | 97 (76.4) | 0.83 (0.73–1.04) | 296 (70.8) | 0.82 (0.68–1.00) |
| Before pregnancy | 23 (18.1) | 1.01 (0.75–1.28) | 93 (22.3) | 0.82 (0.74–1.01)c |
| Before and during | 7 (5.5) | 0.83 (0.67–1.17) | 29 (6.9) | 0.94 (0.76–1.28) |
| Environmental tobacco smoke exposure in the home in the year before pregnancy | ||||
| No | 121 (94.5) | 0.85 (0.74–1.06) | 404 (96.4) | 0.82 (0.69–1.00) |
| Yes | 7 (5.5) | 0.98 (0.63–1.21) | 15 (3.6) | 0.90 (0.77–1.41) |
| Environmental tobacco smoke exposure outside of home in the year before pregnancy | ||||
| No | 74 (57.8) | 0.84 (0.74–1.01) | 261 (62.3) | 0.80 (0.68–0.98) |
| Yes | 54 (42.2) | 0.88 (0.73–1.18) | 158 (37.7) | 0.87 (0.74–1.08) |
| Regular participation in recreational physical activity in year before pregnancy (%) | ||||
| Yes | 109 (85.8) | 0.86 (0.74–1.04) | 386 (92.3) | 0.82 (0.70–1.01) |
| No | 18 (14.2) | 0.93 (0.74–1.22) | 32 (7.7) | 0.84 (0.71–0.93) |
| History of asthma | ||||
| No | 103 (80.5) | 0.86 (0.75–1.11) | 377 (90.2) | 0.83 (0.70–1.01)c |
| Yes | 25 (19.5) | 0.80 (0.68–0.94) | 41 (9.8) | 0.81 (0.71–0.99) |
| History of diabetes (excluding gestational diabetes) | ||||
| No | 119 (93.0) | 0.86 (0.74–1.08) | 406 (97.4) | 0.83 (0.70–1.01) |
| Yes | 9 (7.0) | 0.76 (0.71–0.87) | 11 (2.6) | 0.80 (0.62–0.93) |
| History of chronic hypertension (excluding pregnancy–associated hypertension) | ||||
| No | 107 (83.6) | 0.86 (0.74–1.11) | 405 (96.7) | 0.83 (0.71–1.01)c |
| Yes | 21 (16.4) | 0.84 (0.68–0.98) | 14 (3.3) | 0.80 (0.61–0.94) |
| Multiple gestation | ||||
| No | 112 (87.5) | 0.86 (0.74–1.09) | 409 (97.6) | 0.82 (0.70–1.00)c |
| Yes | 16 (12.5) | 0.82 (0.74–0.99) | 10 (2.4) | 0.84 (0.65–1.01) |
| Year of blood draw | ||||
| 1996–1998 | 42 (32.8) | 1.12 (0.79–1.34) | 74 (17.7) | 1.01 (0.84–1.27) |
| 1999–2001 | 50 (39.1) | 0.84 (0.74–1.00) | 141 (33.7) | 0.84 (0.75–1.01) |
| 2002–2004 | 36 (28.1) | 0.79 (0.70–0.87) | 204 (48.7) | 0.77 (0.64–0.93) |
| Month of blood draw | ||||
| Dec.–Feb. | 32 (25.0) | 0.84 (0.73–1.04) | 92 (22.0) | 0.87 (0.74–1.05) |
| Mar.–May | 24 (18.8) | 0.79 (0.68–0.89) | 106 (25.0) | 0.80 (0.68–0.94) |
| Jun.–Aug. | 37 (28.9) | 0.98 (0.79–1.25) | 111 (26.5) | 0.81 (0.70–1.03)c |
| Sep.–Nov. | 35 (27.3) | 0.86 (0.77–1.05) | 110 (26.3) | 0.84 (0.72–1.01) |
a
IQR = intraquartile range.
b
Numbers in subgroups do not total to overall number due to missing data.
c
Ranksum p-value <0.05 for difference in median carboxyhemoglobin between cases and controls within characteristic stratum.