Table V.
Female BMI and time to pregnancy by age, smoking history, cycle regularity and attempted cycles before study entry
| Characteristic | BMI (kg/m2) |
||||
|---|---|---|---|---|---|
| <20 | 20–24 | 25–29 | 30–34 | ≥35 | |
| Age at baseline | |||||
| <25 | |||||
| No. | 28 | 89 | 32 | 10 | 4 |
| Cycles | 149 | 420 | 212 | 69 | 74 |
| FR (95% CI)a | 0.89 (0.53–1.48) | 1.00 (reference) | 0.73 (0.46–1.16) | 0.35 (0.16–0.76) | 0.21 (0.06–0.76) |
| FR (95% CI)b | 0.90 (0.50–1.60) | 1.00 (reference) | 0.74 (0.41–1.33) | 0.37 (0.15–0.96) | 0.22 (0.05–0.92) |
| 25–29 | |||||
| No. | 73 | 312 | 87 | 45 | 24 |
| Cycles | 415 | 1571 | 529 | 243 | 173 |
| FR (95% CI)a | 0.85 (0.64–1.15) | 1.00 (reference) | 0.83 (0.63–1.09) | 0.91 (0.62–1.32) | 0.68 (0.42–1.11) |
| FR (95% CI)b | 0.95 (0.69–1.31) | 1.00 (reference) | 0.69 (0.50–0.96) | 0.67 (0.41–1.08) | 0.49 (0.28–0.88) |
| ≥30 | |||||
| No. | 60 | 265 | 80 | 30 | 10 |
| Cycles | 279 | 1425 | 437 | 237 | 87 |
| FR (95% CI)a | 1.09 (0.79–1.52) | 1.00 (reference) | 0.94 (0.70–1.25) | 0.67 (0.43–1.04) | 0.67 (0.33–1.36) |
| FR (95% CI)b | 1.16 (0.82–1.65) | 1.00 (reference) | 0.80 (0.57–1.13) | 0.53 (0.31–0.90) | 0.52 (0.24–1.12) |
| Smoking status | |||||
| Ever | |||||
| No. | 49 | 259 | 89 | 37 | 19 |
| Cycles | 267 | 1480 | 521 | 258 | 168 |
| FR (95% CI)a | 1.08 (0.76–1.55) | 1.00 (reference) | 0.93 (0.70–1.23) | 0.86 (0.58–1.27) | 0.79 (0.44–1.41) |
| FR (95% CI)b | 1.14 (0.77–1.68) | 1.00 (reference) | 0.84 (0.61–1.16) | 0.74 (0.45–1.19) | 0.68 (0.36–1.29) |
| Never | |||||
| No. | 112 | 407 | 110 | 48 | 19 |
| Cycles | 576 | 1935 | 657 | 311 | 166 |
| FR (95% CI)a | 0.89 (0.70–1.14) | 1.00 (reference) | 0.75 (0.59–0.95) | 0.73 (0.52–1.04) | 0.49 (0.29–0.81) |
| FR (95% CI)b | 0.96 (0.74–1.25) | 1.00 (reference) | 0.64 (0.47–0.87) | 0.57 (0.34–0.94) | 0.37 (0.19–0.70) |
| Regular cycles | |||||
| No | |||||
| No. | 49 | 147 | 36 | 11 | 6 |
| Cycles | 264 | 754 | 250 | 102 | 85 |
| FR (95% CI)a | 1.05 (0.71–1.54) | 1.00 (reference) | 0.57 (0.37–0.89) | 0.54 (0.26–1.10) | 0.27 (0.10–0.72) |
| FR (95% CI)b | 1.16 (0.76–1.78) | 1.00 (reference) | 0.49 (0.26–0.91) | 0.43 (0.13–1.35) | 0.22 (0.06–0.81) |
| Yes | |||||
| No. | 112 | 519 | 163 | 74 | 32 |
| Cycles | 579 | 2662 | 928 | 467 | 249 |
| FR (95% CI)* | 0.93 (0.74–1.18) | 1.00 (reference) | 0.87 (0.71–1.07) | 0.85 (0.64–1.12) | 0.70 (0.47–1.06) |
| FR (95% CI)b | 1.01 (0.78–1.30) | 1.00 (reference) | 0.76 (0.60–0.96) | 0.68 (0.48–0.97) | 0.56 (0.35–0.88) |
| Cycle attempts before study entry | |||||
| ≤2 | |||||
| No. | 122 | 502 | 148 | 64 | 28 |
| Cycles | 629 | 2418 | 862 | 409 | 244 |
| FR (95% CI)a | 0.90 (0.72–1.13) | 1.00 (reference) | 0.80 (0.65–0.99) | 0.73 (0.54–0.99) | 0.59 (0.38–0.91) |
| FR (95% CI)b | 0.99 (0.77–1.27) | 1.00 (reference) | 0.67 (0.53–0.85) | 0.55 (0.38–0.79) | 0.43 (0.27–0.70) |
| 3–6 | |||||
| No. | 39 | 164 | 51 | 21 | 10 |
| Cycles | 214 | 998 | 316 | 160 | 90 |
| FR (95% CI)a | 1.24 (0.82–1.87) | 1.00 (reference) | 0.86 (0.60–1.25) | 0.76 (0.44–1.32) | 0.70 (0.34–1.47) |
| FR (95% CI)b | 1.29 (0.82–2.04) | 1.00 (reference) | 0.83 (0.52–1.35) | 0.72 (0.30–1.72) | 0.67 (0.26–1.74) |
FR = fecundability ratio; CI = confidence interval; No. = number of pregnancies.
aWhen applicable, adjusted for age, partner's age, cycle regularity, cycle length, partner's BMI, physical activity, smoking, alcohol intake, intercourse frequency and parity.
bAdjusted for all covariates in ‘a’ as well as waist circumference.