Table 3.
The association between birth spacing and the risk of invasive epithelial ovarian cancer in biparous and triparous women
| Birth year < 1935 |
||||
|---|---|---|---|---|
| Birth spacing (months) | Cases/Controls | Crude RR (95% CI) | Adjusted RR (95% CI) | Adjusted RR (95% CI) |
| Biparous women (n=19,810)1 | ||||
| <12 | 12/59 | 1.00 (0.54–1.86) | 0.94 (0.51–1.76) | 1.10 (0.48–2.55) |
| 12–17 | 140/740 | 0.93 (0.77–1.12) | 0.91 (0.75–1.10) | 0.76 (0.56–1.03) |
| 18–23 | 257/1,368 | 0.92 (0.80–1.07) | 0.93 (0.80–1.07) | 0.81 (0.63–1.03) |
| 24–47 | 1,485/7,299 | 1.00 (Reference) | 1.00 (Reference) | 1.00 (Reference) |
| 48–71 | 782/3,915 | 0.98 (0.89–1.08) | 0.96 (0.87–1.05) | 0.92 (0.80–1.06) |
| >=72 | 637/3,116 | 1.01 (0.91–1.11) | 0.95 (0.85–1.05) | 0.90 (0.78–1.05) |
| As a continuous variable 3 | 1.00 (0.99 – 1.02) | 1.00 (0.98 – 1.01) | 0.99 (0.98 – 1.01) | |
| Triparous women (n=9,847)2 | ||||
| Interval between 1st and 2nd childbirth | ||||
| <12 | 8/75 | 0.64 (0.31–1.33) | 0.60 (0.29–1.26) | 1.48 (0.60–3.66) |
| 12–17 | 160/823 | 1.17 (0.97–1.41) | 1.15 (0.95–1.39) | 1.39 (1.07–1.80) |
| 18–23 | 198/1,244 | 0.95 (0.80–1.12) | 0.95 (0.80–1.13) | 0.95 (0.73–1.23) |
| 24–47 | 697/4,136 | 1.00 (Reference) | 1.00 (Reference) | 1.00(Reference) |
| 48–71 | 223/1,332 | 1.00 (0.85–1.18) | 0.97 (0.82–1.14) | 0.96 (0.76–1.21) |
| >=72 | 132/819 | 0.98 (0.80–1.19) | 0.93 (0.76–1.14) | 0.92 (0.69–1.23) |
| As a continuous variable 3 | 1.00 (0.97 – 1.02) | 0.99 (0.96 – 1.02) | 0.98 (0.94 – 1.02) | |
| Interval between 2nd and 3rd childbirth | ||||
| <12 | 2/28 | 0.43 (0.10–1.83) | 0.42 (0.10–1.78) | 1.37 (0.30–6.34) |
| 12–17 | 66/438 | 0.91 (0.69–1.20) | 0.91 (0.69–1.20) | 1.09 (0.74–1.61) |
| 18–23 | 94/697 | 0.81 (0.64–1.03) | 0.81 (0.64–1.03) | 0.84 (0.59–1.19) |
| 24–47 | 426/2,577 | 1.00 (Reference) | 1.00 (Reference) | 1.00(Reference) |
| 48–71 | 359/2,048 | 1.06 (0.91–1.24) | 1.05 (0.90–1.22) | 1.06 (0.84–1.34) |
| >=72 | 471/2,641 | 1.08 (0.94–1.24) | 1.04 (0.90–1.20) | 1.05 (0.85–1.29) |
| As a continuous variable 3 | 1.02 (1.00 – 1.03) | 1.01 (0.99 – 1.03) | 1.01 (0.98 – 1.04) | |
Relative risk (RR) adjusted for age, age at first childbirth, education level, area of residence, and gender of the 1st and 2nd infants.
RR adjusted for age, age at first childbirth, education level, area of residence, gender of the 1st, 2nd, and 3rd infants. The effect estimates for the interval between the 1st and 2nd childbirth and that between 2nd and 3rd childbirth were mutually adjusted for in the same model. 24 subjects had missing data on one or more variables included in the analysis.
Birth spacing (in years) was fitted in the model as a continuous variable and its coefficient was exponentiated to obtain RR associated with each one-year increase in birth spacing.