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  • Title: Pill method failures in women seeking abortion: fourteen years experience.
    Author: Sparrow MJ.
    Journal: N Z Med J; 1998 Oct 09; 111(1075):386-8. PubMed ID: 9830420.
    Abstract:
    AIMS: To document predisposing factors in 769 women who had inadvertently conceived while taking oral contraceptive pills reliably. METHODS: Over a 14-year period, 1981-1995, two questionnaires were administered, one for women using the combined oral contraceptive pill (COC) and one for women using the progestogen only pill (POP). RESULTS: More than one predisposing factor was usually present, the most common being diarrhoea and/or vomiting in 39.0%. Antibiotics had been prescribed in 20.5%. COC failure was associated with a high incidence of menstrual disturbance (37.1%). A history of a previous pill failure was obtained in 27.8%. Smoking was a risk factor for women on the COC. Only 6.0% became pregnant during the first month of pill use. As expected, POP users experienced a higher number of pill failures in proportion to the market share, but excess weight and time of taking did not appear to be risk factors. Most COCs failed according to the numbers expected from the market share. CONCLUSIONS: Many pill failures could be averted by better information about known or suspected risk factors, especially gastrointestinal upset and interacting medications. Pill failure is one more reason to discourage smoking in COC users. Predisposing factors to oral contraceptive (OC) failure in reliable pill takers were investigated in a survey of 769 women who presented to Wellington (New Zealand) Hospital in 1981-95 for induced abortion. More than one predisposing factor was found in the majority of cases of pill failure. The highest percentage (37%) of pill failures occurred in women 20-24 years of age. The most common risk factor was diarrhea and/or vomiting, present around the time of conception in 39% of women. Another 21% took antibiotics during this period. Menstrual disturbance prior to the pregnancy occurred in 37.1%--a rate higher than that expected from studies of pill use. A history of previous pill failure was present in 27.8%. Smoking was a risk factor in users of combined OCs. 33.7% of women using the progestogen-only pill and 34.2% of combined OC users were under severe stress at the time pregnancy occurred. As expected, progestogen-only pill users experienced a higher rate of failure relative to the market share, but excess weight and the time of pill taking were not risk factors. These findings suggest a need for careful counseling about the potential of gastrointestinal illness and interacting medications to compromise pill effectiveness.
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