Researchers conducted this study to test the hypothesis that hospital referral for unexplained abdominal pain might occur less frequently in OC users and more regularly in IUD users than in other women.

The study design was a prospective cohort study of 17 032 women using different methods of contraception.

The outcome measure was a referral to the hospital for unexplained abdominal pain coded to ICD rubric 785.5 in the 8th Revision of the ICD.

The referral was decreased by 13% in current or current users of OCs in comparison with non-users, a difference that just reached statistical significance. No significant difference was found in the corresponding analysis for IUD users. Past users of OCs had much the same risk of referral as non-users. Still, the risk of referral in past users of an IUD was increased at all intervals examined, varying from 17% 13-24 months after discontinuation to 56% 73-96 months after discontinuation. The referral was 29% higher in smokers of 15 or more cigarettes a day than in non-smokers.

The study concluded that referral to hospital for unexplained abdominal pain might be slightly reduced in current or recent OC users and moderately increased in past IUD users. However, the types of IUD used most commonly in the Oxford-FPA study are no longer in current use today. Hospital referral for unexplained abdominal pain seems to be moderately increased in heavy cigarette smokers.