Crude fecundability ratios according to lead exposure and potential confounding factors; univariate Cox discrete proportional hazard models
| Factors | Pregnancy no. | % | Fecundability ratio | 95% CI |
|---|---|---|---|---|
| †Reference category. | ||||
| *p<0.05; **p<0.01; ***p<0.001. | ||||
| ICL, index of cumulative blood lead; TTP, time to pregnancy. | ||||
| Male factors | ||||
| Lead exposure at the beginning of the calendar year when TTP started (μg/dl) | ||||
| Non-exposed† | 153 | 54.6 | 1.00 | |
| <20 | 31 | 11.1 | 0.86 | 0.58 to 1.27 |
| 20–29 | 25 | 8.9 | 0.64* | 0.42 to 0.98 |
| 30–39 | 34 | 12.2 | 0.49*** | 0.34 to 0.72 |
| ⩾40 | 37 | 13.2 | 0.37*** | 0.25 to 0.53 |
| ICL exposure (μg/dl) | ||||
| Non-exposed† | 153 | 54.6 | 1.00 | |
| <80 | 56 | 20.0 | 0.59* | 0.43 to 0.80 |
| 80–149 | 32 | 11.5 | 0.44*** | 0.27 to 0.67 |
| ⩾150 | 39 | 13.9 | 0.36*** | 0.26 to 0.51 |
| Age at the beginning of TTP | ||||
| 18–24 | 46 | 16.4 | 1.34 | 0.95 to 1.90 |
| 25–29† | 128 | 45.7 | 1.00 | |
| 30–38 | 106 | 37.9 | 0.90 | 0.70 to 1.17 |
| Smoking (cigarettes/day) | ||||
| Non-smoker† | 80 | 28.6 | 1.00 | |
| 1–10 | 76 | 27.1 | 1.13 | 0.82 to 1.54 |
| >10 | 124 | 44.3 | 1.04 | 0.78 to 1.38 |
| Use of alcohol (drinks/week) | ||||
| <1† | 174 | 62.1 | 1.00 | |
| 1–2 | 80 | 28.6 | 0.91 | 0.70 to 1.17 |
| ⩾3 | 26 | 9.3 | 1.12 | 0.74 to 1.69 |
| Use of tea or coffee (cups/day) | ||||
| <1† | 170 | 60.7 | 1.00 | |
| 1–2 | 78 | 27.9 | 0.98 | 0.74 to 1.27 |
| ⩾3 | 32 | 11.4 | 0.99 | 0.68 to 1.44 |
| Female factors | ||||
| Age at the beginning of TTP | ||||
| 18–24 | 115 | 41.1 | 0.95 | 0.67 to 1.36 |
| 25–29† | 124 | 44.3 | 1.00 | |
| 30–34 | 41 | 14.6 | 0.88 | 0.46 to 1.59 |
| Lead exposure at the beginning of the calendar year when TTP started | ||||
| No† | 263 | 93.9 | 1.00 | |
| Yes | 17 | 6.1 | 0.59* | 0.36 to 0.96 |
| Shift work | ||||
| No† | 264 | 94.3 | 1.00 | |
| Yes | 16 | 5.7 | 0.72 | 0.39 to 1.33 |
| Smoking (cigarettes/day) | ||||
| Non-smoker† | 241 | 86.1 | 1.00 | |
| 1–10 | 39 | 13.9 | 0.93 | 0.66 to 1.31 |
| Use of alcohol (times/week) | ||||
| <1† | 235 | 83.9 | 1.00 | |
| 1–2 | 45 | 16.1 | 1.11 | 0.81 to 1.52 |
| Use of tea or coffee (cups/day) | ||||
| <1† | 220 | 78.6 | 1.00 | |
| 1–2 | 39 | 13.9 | 1.19 | 0.84 to 1.67 |
| ⩾3 | 21 | 7.5 | 1.29 | 0.82 to 2.02 |
| Menarche (years) | ||||
| ⩽13 | 50 | 17.9 | 1.28 | 0.94 to 1.75 |
| 14–16† | 214 | 76.4 | 1.00 | |
| ⩾17 | 16 | 5.7 | 1.04 | 0.63 to 1.73 |
| Contraceptive use before TTP | ||||
| Intrauterine device | 35 | 12.5 | 0.77 | 0.49 to 1.08 |
| Pill | 25 | 8.9 | 0.86 | 0.50 to 1.21 |
| Condom | 96 | 34.3 | 1.04 | 0.78 to 1.13 |
| None† | 124 | 44.3 | 1.00 | |
| Year of the pregnancy | ||||
| 1985–89 | 75 | 26.8 | 0.98 | 0.73 to 1.33 |
| 1990–94† | 102 | 36.4 | 1.00 | |
| 1995–99 | 103 | 36.8 | 0.78 | 0.59 to 1.02 |
| Sequence of the pregnancy | ||||
| 1† | 115 | 41.1 | 1.00 | |
| ⩾2 | 165 | 58.9 | 0.79 | 0.62 to 1.03 |