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. Author manuscript; available in PMC: 2020 Oct 15.
Published in final edited form as: Int J Cancer. 2017 Sep 12;141(12):2392–2399. doi: 10.1002/ijc.30910

Table 4.

Relative risks (95% CIs) for births, age at first birth (per 5 years category) and oral contraceptive (COC) use (5 years of use) and risk of ovarian cancer, by histotype1

No. of cases Births, per birth2,3 Age at first birth2,3 COC use2,4 COC use <35 yrs2,4 COC use 35+ yrs2,4
All women1 (n = 1,632) 0.87 (0.83–0.92) 0.87 (0.82–0.93) 0.72 (0.67–0.77) 0.66 (0.59–0.73) 0.86 (0.73–1.01)
HGSOC2 (n = 559) 0.89 (0.83–0.96) 0.94 (0.86–1.04) 0.72 (0.64–0.80) 0.67 (0.57–0.79) 0.80 (0.63–1.02)
LGSOC2 (n = 207) 0.93 (0.84–1.04) 0.87 (0.75–1.01) 0.69 (0.57–0.83) 0.65 (0.51–0.84) 0.78 (0.51–1.21)
Endometroid (n = 192) 0.83 (0.74–0.93) 0.82 (0.70–0.95) 0.69 (0.58–0.83) 0.62 (0.49–0.79) 0.88 (0.60–1.29)
Clear Cell (n = 87) 0.72 (0.58–0.88) 0.74 (0.57–0.96) 0.64 (0.49–0.84) 0.66 (0.46–0.93) 0.61 (0.30–1.25)
Mucinous (n = 119) 0.82 (0.71–0.96) 0.89 (0.74–1.08) 0.79 (0.64–0.98) 0.73 (0.54–0.97) 0.98 (0.60–1.60)
1

Numbers do not sum to total due to missing histotype.

2

Stratified analysis (see Methods) and adjusted for the basic factor set (see footnote to Table 1).

3

Also adjusted for duration of COC use at ages <35 years (continuous) and 35+ yrs (continuous).

4

Also adjusted for number of births (continuous) and age at first birth category (continuous).

Abbreviations: HGSOC, high grade serous ovarian cancer; LGSOC, low grade serous ovarian cancer.