Prolonged use of oral contraception before a planned pregnancy is associated with a decreased risk of delayed conception.

BACKGROUND The aim of this study was to investigate the association of total duration of oral contraceptive usage with time to conception. METHODS This was a prospective study of 8497 planned pregnancies drawn from a population that recruited 85% of eligible couples in South-West England who were expecting a baby in a 21 month period. Self-completion questionnaires were administered at 18 weeks gestation to ascertain parity, paternity, co-habitation, use of the contraceptive pill, smoking and alcohol status, educational achievement, height, weight and time taken to conceive. Logistic regression was used to identify factors independently related to conception in < or =12 months. RESULTS Of the participants, 74% conceived in < or =6 months, 14% in 6-12 months and 12% after 1 year. Previous prolonged oral contraceptive usage was statistically significantly associated with a decreased risk of delayed conception. Prolonged use of oral contraception was also associated with improved fecundity independent of other factors. Selection bias due to particularly fertile women using oral contraceptives is unlikely because similar odds ratios were calculated for nulligravid women. CONCLUSIONS Women who have prolonged use of oral contraceptives might be reassured that they will not be disadvantaged in terms of time taken to achieve conception.