Table 3.
Relative risk of endometrial cancer after a pregnancy compared with having one pregnancy less by pregnancy number and type, stratified by age at pregnancy, time since pregnancy, and attained age at diagnosis
| Pregnancy No and type | Adjusted relative risk (95% CI)* | |
|---|---|---|
| Age at pregnancy† | <30 years | ≥30 years |
| First pregnancy: | ||
| Induced abortion | 0.59 (0.48 to 0.72) | 0.42 (0.30 to 0.61) |
| Childbirth | 0.67 (0.62 to 0.73) | 0.61 (0.55 to 0.69) |
| Any subsequent: | ||
| Induced abortion | 0.90 (0.80 to 1.01) | 0.78 (0.73 to 0.84) |
| Childbirth | 0.89 (0.86 to 0.92) | 0.79 (0.75 to 0.83) |
| Time since pregnancy‡ | <10 years | ≥10 years |
| First pregnancy: | ||
| Induced abortion | 0.36 (0.13 to 0.97) | 0.56 (0.47 to 0.67) |
| Childbirth | 0.33 (0.23 to 0.50) | 0.68 (0.62 to 0.73) |
| Any subsequent: | ||
| Induced abortion | 0.45 (0.32 to 0.62) | 0.84 (0.79 to 0.89) |
| Childbirth | 0.45 (0.36 to 0.56) | 0.87 (0.84 to 0.90) |
| Attained age§ | <50 years | ≥50 years |
| First pregnancy: | ||
| Induced abortion | 0.40 (0.28 to 0.56) | 0.61 (0.49 to 0.75) |
| Childbirth | 0.42 (0.35 to 0.51) | 0.73 (0.67 to 0.80) |
| Any subsequent: | ||
| Induced abortion | 0.80 (0.68 to 0.94) | 0.82 (0.77 to 0.87) |
| Childbirth | 0.73 (0.67 to 0.81) | 0.88 (0.85 to 0.91) |
Adjusted for age, period, educational attainment, marital status, urbanicity, and interaction between period and age, educational attainment, marital status, and urbanicity, respectively. Test for difference in fit when stratifying by age at pregnancy, time since pregnancy, and attained age, respectively, compared with analysis in table 1, P=0.69, P=0.94, and P=0.13, respectively.
5215 events and 32 745 464 person years among women with a pregnancy before age 30 years, and 2462 events and 15 465 953 person years among women with a pregnancy at or after age 30 years.
123 events and 16 813 543 person years among women with less than 10 years since pregnancy, and 5681 events and 26 026 430 person years among women with less than 10 years since pregnancy.
929 events and 46 156 519 person years among women aged less than 50 years, and 5814 events and 11 191 103 person years among women aged 50 or more years.