Table 2.
Error in recalled time-to-pregnancy: 421 women in the first trimester, The Snart-Gravid Study, Denmark, 2007–2012.
| N | Under-estimateda % (95% CI) | Over-estimatedb % (95% CI) | Recall Error, monthsc
|
||
|---|---|---|---|---|---|
| Mean (95% CI) | Mean Differenced (95% CI) | ||||
| Entire population | 421 | 26 (95% CI 22, 30) | 21 (95% CI 17, 24) | −0.11 (95% CI −0.25, 0.04) | -- |
| Prospective TTP | |||||
| ≤2 | 219 | 13 (95% CI 8, 17) | 22 (95% CI 16, 27) | 0.11 (95% CI 0.03, 0.19) | 0.00 (reference) |
| >2 | 202 | 43 (95% CI 36, 49) | 18 (95% CI 13, 24) | −0.29 (95% CI −0.59, 0.01) | −0.40 (95% CI −0.71, −0.09) |
| Cycle Regularity | |||||
| Regular | 337 | 26 (95% CI 22, 31) | 22 (95% CI 18, 27) | −0.03 (95% CI −0.21, 0.15) | 0.00 (reference) |
| Irregular | 84 | 30 (95% CI 20, 40) | 12 (95% CI 5, 19) | −0.31 (95% CI −0.55, −0.07) | −0.28 (95% CI −0.58, 0.02) |
| Age | |||||
| <30 | 259 | 24 (95% CI 19, 29) | 20 (95% CI 14, 27) | −0.09 (95% CI −0.22, 0.04) | 0.00 (reference) |
| ≥30 | 162 | 32 (95% CI 25, 39) | 20 (95% CI 14, 27) | −0.07 (95% CI −0.41, 0.27) | 0.01 (95% CI −0.34, 0.38) |
| Gravidity | |||||
| Nulligravid | 221 | 27 (95% CI 21, 33) | 22 (95% CI 16, 27) | −0.07 (95% CI −0.19, 0.05) | 0.00 (reference) |
| Gravid | 200 | 27 (95% CI 21, 33) | 19 (95% CI 13, 24) | −0.10 (95% CI −0.38, 0.19) | −0.02 (95% CI −0.34,0.29) |
| Last contraceptive methode | |||||
| Barrier methods | 139 | 25 (95% CI 18, 32) | 16 (95% CI 10, 22) | −0.03 (95% CI −0.40, 0.35) | 0.00 reference) |
| Oral contraceptive | 247 | 26 (95% CI 20, 31) | 25 (95% CI 19, 30) | −0.07 (95% CI −0.20, 0.07) | −0.04 (95% CI −0.36, 0.28) |
TTP=time-to-pregnancy; CI=confidence interval
a
Under-estimated by ≥1 month
b
Over-estimated by ≥1 month
c
Recall error in months calculated as follows: Retrospectively-measured TTP – Prospectively-measured TTP
d
Mean difference in error was estimated from a simple linear regression model.
e
Analysis excluded 35 women whose last contraception was not oral contraceptives or barrier methods.