Table 2.
Association of Baseline and Time-varying caffeine and beverage consumption with time to pregnancy (censored at 12 cycles)
| Results using Beverage Data at Baseline | Results using Time-varying Data on Beverages | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No. pregnancies |
Cycles at Risk |
Unadjusted | Adjusteda | No. pregnancies |
Cycles at risk |
Unadjusted | Adjusteda | ||||||
| FR | (95% CI) | FR | (95% CI) | FR | (95% CI) | FR | (95% CI) | ||||||
| Caffeine (mg/day) | |||||||||||||
| <100b | 1318 | 8233 | 1.00 | 1.00 | 1360 | 8396 | 1.00 | 1.00 | |||||
| 100–199 | 553 | 3300 | 1.06 | (0.95–1.19) | 1.05 | (0.93–1.17) | 544 | 3389 | 1.00 | (0.90–1.12) | 0.98 | (0.88–1.10) | |
| 200–299 | 299 | 1763 | 1.07 | (0.93–1.23) | 1.08 | (0.93–1.25) | 280 | 1613 | 1.06 | (0.91–1.22) | 1.07 | (0.92–1.24) | |
| 300+ | 314 | 1929 | 1.03 | (0.90–1.19) | 1.06 | (0.92–1.23) | 300 | 1827 | 1.01 | (0.88–1.16) | 1.04 | (0.90–1.21) | |
| Coffee (servings/day) | |||||||||||||
| Noneb | |||||||||||||
| <1 | 1001 | 6403 | 1.00 | 1.00 | 1018 | 6445 | 1.00 | 1.00 | |||||
| 1 | 710 | 4307 | 1.06 | (0.95–1.18) | 1.04 | (0.93–1.16) | 709 | 4307 | 1.05 | (0.95–1.17) | 1.03 | (0.92–1.15) | |
| 2 | 431 | 2452 | 1.14 | (1.00–1.29) | 1.13 | (0.99–1.29) | 420 | 2440 | 1.10 | (0.97–1.25) | 1.08 | (0.95–1.24) | |
| 3+ | 235 | 1361 | 1.14 | (0.97–1.33) | 1.18 | (1.00–1.40) | 232 | 1383 | 1.09 | (0.93–1.27) | 1.11 | (0.94–1.31) | |
| 107 | 702 | 0.97 | (0.78–1.21) | 1.01 | (0.80–1.27) | 105 | 650 | 1.01 | (0.81–1.26) | 1.05 | (0.83–1.33) | ||
| Tea (servings/day) | |||||||||||||
| Noneb | 1131 | 7915 | 1.00 | 1.00 | 1272 | 8238 | 1.00 | 1.00 | |||||
| <1 | 984 | 5757 | 1.11 | (1.01–1.22) | 1.10 | (1.00–1.22) | 951 | 5463 | 1.12 | (1.02–1.23) | 1.11 | (1.01–1.22) | |
| 1 | 179 | 1060 | 1.08 | (0.91–1.29) | 1.08 | (0.91–1.29) | 177 | 1065 | 1.06 | (0.89–1.26) | 1.04 | (0.87–1.24) | |
| 2+ | 90 | 493 | 1.19 | (0.93–1.53) | 1.27 | (0.99–1.64) | 84 | 459 | 1.20 | (0.93–1.54) | 1.27 | (0.98–1.64) | |
| Herbal/green tea (servings/day) | |||||||||||||
| Noneb | |||||||||||||
| <1 | 1498 | 9208 | 1.00 | 1.00 | 1500 | 9376 | 1.00 | 1.00 | |||||
| 1 | 718 | 4505 | 0.97 | (0.88–1.08) | 0.93 | (0.84–1.03) | 712 | 4256 | 1.02 | (0.93–1.13) | 0.98 | (0.89–1.09) | |
| 2+ | 174 | 982 | 1.07 | (0.89–1.27) | 1.03 | (0.86–1.23) | 173 | 1035 | 1.02 | (0.85–1.21) | 0.97 | (0.81–1.16) | |
| 94 | 530 | 1.06 | (0.84–1.34) | 1.07 | (0.84–1.35) | 99 | 558 | 1.09 | (0.86–1.36) | 1.07 | (0.85–1.35) | ||
| Cola (servings/day) | |||||||||||||
| Noneb | |||||||||||||
| <1 | 846 | 4886 | 1.00 | 1.00 | 880 | 5131 | 1.00 | 1.00 | |||||
| 1 | 1449 | 9124 | 0.90 | (0.82–0.99) | 0.92 | (0.83–1.01) | 1420 | 8896 | 0.90 | (0.82–0.99) | 0.92 | (0.84–1.02) | |
| 2+ | 153 | 950 | 0.91 | (0.75–1.10) | 0.97 | (0.80–1.18) | 157 | 964 | 0.94 | (0.78–1.14) | 1.01 | (0.83–1.23) | |
| 36 | 265 | 0.78 | (0.54–1.13) | 0.92 | (0.64–1.34) | 27 | 234 | 0.63 | (0.42–0.95) | 0.75 | (0.49–1.13) | ||
| Other soda (servings /day) | |||||||||||||
| Noneb | |||||||||||||
| <1 | 1834 | 10945 | 1.00 | 1.00 | 1841 | 11061 | 1.00 | 1.00 | |||||
| 1 | 636 | 4155 | 0.92 | (0.83–1.01) | 0.94 | (0.85–1.04) | 624 | 4000 | 0.93 | (0.84–1.03) | 0.95 | (0.86–1.05) | |
| 2+ | 11 | 106 | 0.58 | (0.31–1.08) | 0.59 | (0.32–1.11) | 17 | 132 | 0.79 | (0.47–1.32) | 0.81 | (0.48–1.36) | |
| 3 | 19 | 0.96 | (0.28–3.32) | 1.22 | (0.35–4.26) | 2 | 32 | 0.38 | (0.09–1.59) | 0.48 | (0.11–2.01) | ||
| Sweetened sodas (servings/day) | |||||||||||||
| Noneb | |||||||||||||
| <1 | 1506 | 8810 | 1.00 | 1.00 | 1508 | 8813 | 1.00 | 1.00 | |||||
| 1 | 929 | 6035 | 0.90 | (0.82–0.99) | 0.91 | (0.83–1.00) | 929 | 5992 | 0.89 | (0.82–0.98) | 0.91 | (0.83–1.00) | |
| 2+ | 40 | 316 | 0.73 | (0.52–1.03) | 0.77 | (0.55–1.09) | 41 | 352 | 0.68 | (0.49–0.95) | 0.72 | (0.52–1.01) | |
| 9 | 64 | 0.84 | (0.41–1.70) | 0.97 | (0.47–2.00) | 6 | 68 | 0.51 | (0.22–1.18) | 0.58 | (0.25–1.36) | ||
| Diet soda (servings/day) | |||||||||||||
| Noneb | 1306 | 7895 | 1.00 | 1.00 | 1347 | 8147 | 1.00 | 1.00 | |||||
| <1 | 1018 | 6311 | 0.97 | (0.89–1.06) | 0.99 | (0.90–1.09) | 980 | 6100 | 0.96 | (0.87–1.05) | 0.97 | (0.88–1.07) | |
| 1 | 131 | 794 | 0.99 | (0.81–1.21) | 1.02 | (0.83–1.25) | 133 | 782 | 1.03 | (0.85–1.26) | 1.07 | (0.88–1.32) | |
| 2+ | 29 | 225 | 0.77 | (0.52–1.15) | 0.87 | (0.58–1.30) | 24 | 196 | 0.70 | (0.46–1.09) | 0.79 | (0.51–1.23) | |
| All sodas (servings/day) | |||||||||||||
| Noneb | 654 | 3647 | 1.00 | 1.00 | 689 | 3861 | 1.00 | 1.00 | |||||
| <1 | 1600 | 9991 | 0.88 | (0.80–0.98) | 0.90 | (0.81–1.00) | 1570 | 9799 | 0.87 | (0.79–0.96) | 0.89 | (0.80–0.98) | |
| 1 | 184 | 1266 | 0.79 | (0.66–0.95) | 0.83 | (0.69–1.00) | 187 | 1252 | 0.81 | (0.68–0.97) | 0.85 | (0.71–1.02) | |
| 2 | 35 | 243 | 0.80 | (0.55–1.18) | 0.88 | (0.60–1.29) | 32 | 231 | 0.75 | (0.51–1.11) | 0.84 | (0.57–1.25) | |
| 3+ | 11 | 78 | 0.81 | (0.41–1.61) | 1.10 | (0.55–2.21) | 6 | 82 | 0.39 | (0.17–0.91) | 0.48 | (0.21–1.13) | |
a
Adjusted for age at baseline, partner’s age at baseline, parity, BMI, METs/week, pack-years of smoking, alcoholic beverages consumed/week, and intercourse frequency. Estimates for coffee, tea, and colas are mutually adjusted for each other in addition to the other covariates.
b
Reference category.
FR indicates fecundability ratio (cycle-specific probability of conception comparing exposed to unexposed); CI, confidence interval