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In this new occasional seriesthe Faculty of Family Planning and Reproductive Health Care shares answers it has given to questions from experienced family planning clinicians

For women who wish to use the COC, are pills containing 20µg ethinylestradiol as effective as those with higher doses of oestrogen?

The formulations of COCs have changed since they were originally developed. The first combined pill, in the 1960s, contained a high dose of mestranol and norethynodrel. Norethynodrel represented one of the first generation of progestogens (which also includes norethisterone). A second generation progestogen, levonorgestrel, was developed around 1970. From 1994, third-generation progestogens from the gonane class (including desogestrel, gestodene and norgestimate) were used in combined pills in an attempt to reduce androgenic and metabolic effects.

Also, the dose of oestrogen was reduced to minimise the risk of thromboembolism. The estrogen dose has been reduced stepwise from 150µg to 50µg and more recently to 35, 30, 20 and even 15µg1.Even in controlled clinical trials, it is difficult to measure the true efficacy of an oral contraceptive. Two techniques are widely used to quantify contraceptive failure rates: the Pearl Index and life table analysis. The Pearl Index represents the number of failures (unintended pregnancies) per 100 woman-years of exposure. A weakness of this approach is that studies of longer duration result in lower Pearl indices, which may under-represent the true failure rate2-4. The clinical effectiveness unit (CEU) was unable to find any review that compared failure rates (calculated by either method) of different combined oral contraceptives.Advice from the FFPRHC is that when starting a combined pill for the first time, a pill containing 30-35µg ethinyloestradiol (with levonorgestrel or norethisterone) should generally be chosen5. After counselling on the risk of VTE, pills containing desogestrel or gestodene may be used if a woman expresses a preference. The risk of VTE does not vary with the dose of ethinyloestradiol when this dose is less than 50µg.A double-blind, randomised, multicentre trial compared efficacy, cycle control and adverse effects of two combined pills (containing either 20 or 30µg of ethinyloestradiol with 150µg desogestrel). Both formulations were found to have high contraceptive efficacy and to be well tolerated. But cycle control was less consistent with the 20µg pill6. Another study from the same group demonstrated greater alteration in serum lipid profiles with the 30µg pill compared with the 20µg version7.Thus, the CEU was unable to find any strong evidence that failure rates of COCs increase with decreasing oestrogen dose. Currently, the CEU continues to recommend a 30-35µg ethinylestradiol pill as first-line.

What is the risk of ovulation for women starting hormonal contraception up to and including day five of the menstrual cycle, without additional protection?

The WHO Selected Practice Recommendations advises that the COC and the POP can be started up to and including day five of the cycle without the need for additional contraception. Progestogen-only implants and injectables can be started up to and including day seven. The risk of ovulation was felt to be negligible with these starting regimens.

Relaxing the accepted start days for hormonal methods in this way may facilitate the use of effective methods by many couples, particularly in developing countries, but may lead to unintended pregnancies in a small number of women. To minimise any risk, and after counselling on cycle length and timing of ovulation, some women may choose to use a barrier method as back-up when starting hormonal contraception on any day other than one or two.The CEU identified little evidence to contradict WHO. However, we acknowledge that direct or indirect evidence is scarce. Wide variations in cycle length and timing of ovulation occur between individuals. Evidence indicates that when a COC is started up to day seven of the cycle, despite an increase in follicular size, ovulation does not ensue8,9.Theoretically, women with short cycles may be at risk of ovulation with late-start regimens; there are few data to provide an estimate of the proportion of women to whom this might apply. Clinicians should discuss the evidence to allow women to make informed decisions about back-up contraception. Given the paucity of data, clinicians and women may choose to err on the side of caution. Nevertheless, women who prefer not to use a back-up method may be assured that the risk of ovulation is negligible when starting a hormonal method up to and including day five.

These question and answers are from Family Planning Masterclass: Evidence-based Answers to 1,000 questions edited by Gillian Penney, Susan Brechin and Anna Glasier, published by the Royal College of Obstetricians and Gynaecologists, 2006, priced £48. ISBN 1-904752-33-0. To order a copy go to www.rcogbookshop.com

References

1 Cerel-Suhl SL, Yeager BF. Update on oral contraceptive pills. Am Fam Phys 1999;60:2073-842 Hatcher RA et al. Contraceptive technology. New York: Ardent Media; 19983 Trussell J, Kost K. Contraceptive failure in the US: a critical review of the literature. Stud Fam Plann 1987;18:237-834 Trussell J. Methodological pitfalls in the analysis of contraceptive failure. Stat Med 1991;10:201-205 FFPRC Clinical Effectiveness Unit. First prescription of combined oral contraception. J Fam Plann Reprod Health Care 2003;29:209-226 Akerlund M et al. Comparative profiles of reliability, cycle control and adverse effects of two oral contraceptive formulations containing 150µg desogestrel and either 30µg or 20µg ethinyloestradiol. Br J Obstet Gynaecol 1993;100:832-887 Akerlund M et al. Oral contraceptive tables containing 20 and 30µg of ethinyloestradiol with 150µg desogestrel. Their influence on lipids, lipoproteins, sex hormone binding globulin and testosterone. Acta Obstet Gynecol Scand 1994;73:136-438 Smith SK et al. The effect of deliberate omission of trinordiol or microgynon on the hypothalamo-pituitary-ovarian axis. Contraception 1986;34:513-229 Killick SR et al. Extending the duration of the pill-free interval during combined oral contraception. Adv Contracept 1990;6:33-40

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