Parity as a risk factor for cervical cancer.

In a case-control study of 759 invasive cervical cancer patients and 1,430 controls in Colombia, Costa Rica, Mexico, and Panama conducted during 1986-1987, an association with number of pregnancies persisted after adjustment for sexual and socioeconomic variables. Risks rose steadily to 5.1 (95% confidence interval 2.7-9.7) for those with 14 or more pregnancies and a relation of risk to multiparity was observed in all four study countries. Pregnancy associations appeared to relate to the number of live births rather than to miscarriages or abortions, with multiparity relations most pronounced among premenopausal women and oral contraceptive users. Human papillomaviruses types 16 and 18, as measured by filter in situ hybridization, were not significantly associated with number of births and did not explain the strong relation of parity to risk. Our results indicate the need for further consideration of reproductive factors on cervical cancer risk, with attention given to possible mechanisms of action, including hormonal factors and cervical trauma.