Does being pregnant reduce risk of ovarian cancer?

Answer 1

There seems to be some correlation. I did a quick search, (+pregnancy "ovarian cancer risk) and found the following:

Reproductive history: Women who started menstruating at an early age (before age 12), had no children or had their first child after age 30, and/or experienced menopause after age 50 may have an increased risk of ovarian cancer. There seems to be a relationship between the number of menstrual cycles in a woman's lifetime and her risk of developing ovarian cancer.

http://www.cancer.org/docroot/CRI/content/CRI_2_4_2X_What_are_the_risk_factors_for_ovarian_cancer_33.asp?sitearea

I also found this:

The risk for developing ovarian cancer appears to be affected by several factors. The more children a woman has, the lower her risk of ovarian cancer. Early age at first pregnancy, older ages of final pregnancy and the use of low dose oral contraceptive pills have also been shown to have a protective effect. Ovarian cancer is reduced in women after tubal ligation.

http://en.wikipedia.org/wiki/Ovarian_cancer

Answer 2

I would think so given that preventing ovulation reduces the risk of ovarian cancer. that's why the birth control pill is beneficial.

Answer 3

possible, because the risk factors of the disease are infertility, nulliparity (a woman who has not given birth to a viable infant)
delayed childbearing and spontaneous abortion.

Answer 4

Yes, and breast cancer too.