Adjusted fecundity ratio according to lead exposure and confounding factors; multivariable Cox discrete proportional hazard models
| Factors | All valid pregnancies | One randomly selected pregnancy | Restricted to the first pregnancy | |||
|---|---|---|---|---|---|---|
| No. | FR (95%CI) | No. | FR (95%CI) | No. | FR (95%CI) | |
| †Reference category. | ||||||
| ‡p = 0.06; *p<0.05; ***<0.001. | ||||||
| Adjusted with paternal and maternal lead exposure at the beginning of calendar year when TTP started, maternal age at the beginning of TTP, and pregnancy sequence (all valid pregnancies). | ||||||
| FR, fecundability ratio; TTP, time to pregnancy. | ||||||
| Male factors | ||||||
| Lead exposure at the beginning of the calendar year when TTP started (μg/dl) | ||||||
| Non-exposed† | 153 | 1.00 | 65 | 1.00 | 67 | 1.00 |
| <20 | 31 | 0.91 (0.61 to 1.35) | 21 | 0.88 (0.54 to 1.44) | 17 | 0.88 (0.50 to 1.53) |
| 20 to 29 | 25 | 0.71 (0.46 to 1.09) | 15 | 0.66 (0.38 to 1.16) | 13 | 0.62 (0.33 to 1.14) |
| 30 to 39 | 34 | 0.50* (0.34 to 0.74) | 17 | 0.50* (0.29 to 0.89) | 11 | 0.52* (0.27 to 0.99) |
| ⩾40 | 37 | 0.38*** (0.26 to 0.56) | 15 | 0.37*** (0.22 to 0.64) | 7 | 0.48* (0.23 to 0.78) |
| Female factors | ||||||
| Lead exposure at the beginning of the calendar year when TTP started | ||||||
| No† | 263 | 1.00 | 124 | 1.00 | 106 | 1.00 |
| Yes | 17 | 0.61‡ (0.37 to 1.01) | 9 | 0.62 (0.31 to 1.25) | 9 | 0.69 (0.34 to 1.40) |
| Age at the beginning of TTP | ||||||
| 18 to 24 | 115 | 1.29 (0.98 to 1.70) | 53 | 1.28 (0.88 to 1.88) | 65 | 0.95 (0.64 to 1.41) |
| 25 to 29† | 124 | 1.00 | 60 | 1.00 | 44 | 1.00 |
| 30 to 34 | 41 | 0.83 (0.58 to 1.20) | 20 | 0.76 (0.43 to 1.37) | 6 | 0.57 (0.22 to 1.50) |
| Sequence of the pregnancy | ||||||
| 1† | 115 | 1.00 | ||||
| ⩾2 | 165 | 1.07 (0.83 to 1.38) | ||||