Reproductive Factors

Although, the precise cause of EOC is unknown, several theories exist. The theory of "incessant ovulation" speculates that trauma to the ovarian surface epithelium during ovulation predisposes to malignant transformation. Accordingly, those with long periods of uninterrupted ovulations, such as nulliparous women (9), and those with early menarche or late menopause (10) have an increased risk for developing EOC. Higher risk has also been documented among infertile women (11-14), and some investigators have noted that drugs to induce ovulation, such as clomiphene citrate, have also been associated with an increased risk (14,15) (Table 2).

In contrast, several factors interrupting long periods of ovulation have been reported to decrease the risk of EOC. Multiparity is one such protective factor: women with one pregnancy have a relative risk of 0.6-0.8, and each subsequent pregnancy might lower the risk by about 10-15% (11,14,16-19). Breastfeeding has also been shown to confer some decrease in risk (16,20-22), although most studies show no correlation with length of lactation. In particular, use of oral contraceptives is associated with a dramatic reduction in risk. Studies have reported a decrease in risk by about 40-50% with any duration of use (23-25), but the protection is the most pronounced with long-term use. One study noted a reduction in risk of 80% with 10 years or more of use (26).

Previous hysterectomy has been associated with a lowered risk for ovarian cancer with odds ratios ranging from 0.58 to 0.78 (16-18,27-30). Annegers et al. (27) noted

Table 2

Reproductive Risk Factors for Development of Epithelial Ovarian Cancer

Factor Odds ratio

Parity (14)

0 term pregnancies 1

1 term pregnancy 0.6

2 term pregnancies 0.53

3 term pregnancies 0.48 >3 term pregnancies 0.36-0.29

Early menarche (10)

Age 13 1

Age <13 1.13 Late menopause (10)

Age 45 1

Age 45-49 1.25

Age 50-53 1.40

Age 53 1.58 Contraception (25)

No use 1

Any use oral contraceptives 0.6

Any use IUD 0.8

Any use barrier methods 0.8

Tubal ligation 0.5 Length of oral contraceptive use (26)

Never 1

3-6 months 0.6

7-11 months 0.7

>9 years 0.2 Breastfeeding (22)

Never 1

Ever 0.5 Infertility (13)

<2 years unprotected intercourse 1

>10 years unprotected intercourse 1.8

Previous hysterectomy (29) 0.58

that this reduction in risk was apparent even when one or both ovaries were preserved. This effect was present for 20-25 years (18,28). Surgical tubal ligation has been associated with reduction in ovarian cancer risk (16,17,25,28,29). Ness et al. (25) found that several methods of contraception (including oral contraceptives, intrauterine devices, barrier methods, and tubal ligation) were associated with reduced risk for ovarian cancer, even after adjustment for age, race, parity, and family history.

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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