OC failure rates

An estimated 75 million women use COCs.

Dinger et al reported on failure rates in 112,659 woman-years.

The study population comprised 59,000 European women followed up to 5 years.

There were 545 unplanned pregnancies (0.48376 - call it 0.5 - per 100 woman years, i.e. a Pearl_Index of 0.5).

The failure rate was highest in younger women and lowest in women over 29 years.

Failures were most common in the first year the failure rate declined in each of the subsequent years.

Failure rates were not influenced by:

    BMI

    type and dose of OC

Possible causes of the failures were:

    inappropriate use:            42.2%

    vomiting & diarrhoea:      18.3%

    antibiotic use:                   15.6%