Primary infertility and oral contraceptive steroid use.

Objective: To determine the association between combined monophasic oral contraceptive (OC) use and primary infertility.

Design: Case-control.

Setting: Women serving as controls of the Cancer and Steroid Hormone Study.

Participants: Women were 19 to 40 years of age at first conception or infertility diagnosis. Based on 24 consecutive months of unprotected intercourse without a recognized conception, 419 nulligravid women had primary infertility; controls were 2,120 fertile women. A calendar of each women's reproductive history was used to determine fertility status and contraceptive use before infertility diagnosis or first conception.

Main Outcome Measure: Primary infertility.

Results: Combined monophasic OC use was associated with a lower frequency of primary infertility, particularly among younger (age 20 years) compared with older women (age 30 years) after adjusting for barrier method use and education. A similar association was found for duration of OC use. When adjusted for age at first conception or infertility and barrier method, both higher (> 50 micrograms) and lower (< or = 50 micrograms) estrogen dose use were associated with decreased risk of primary infertility.

Conclusion: Combined monophasic OC use was associated with a lower frequency of primary infertility.