RATIONALE FOR MODIFYING THE 7-DAY HORMONE-FREE INTERVAL Risk of Escape Ovulation

display, view an d print a single c opy for persona l use Oral contraceptives are used by millions of women worldwide, and are the most common form of birth control chosen by Canadi n women.1 In Canada, 18% of women aged 15-49 use the combined oral contraceptive (COC), and of Canadian women who use contraception, 32% choose COCs as their primary form of birth control.2,3 Since the introduction of the first COC in 1960, COCs have undergone many modifications. Most notably, the amount of estrogen has declined steadily over the years, with today’s low-dose COCs containing ≤ 35μg ethinyl estradiol (EE). In addition, new progestins—with varying degrees of progestational potency, as well as estrogenic, anti-estrogenic, or androgenic activity—have emerged over the past 50 years. Depending on the COC, the amount of estrogen and/or progestin may be varied weekly.1 In Canada, one aspect of the COC that has undergone limited modification is the way in which COCs are dosed. COCs were originally designed to be taken for 21 days, followed by a seven-day hormone-free interval (HFI). While the reasons for choosing an HFI of seven days may have been more happenstance than scientific dictum, the 21/7 dosing regimen has become the standard dosing regimen for OCs.4 Over time, women have come to take the 21/7 dosing regimen for granted. Suppression of menstruation through elimination of the HFI is one modification to the dosing regimen that has been used in the medical community for many years, and is gaining acceptance among Canadian women. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recognizes the use of continuous and extended combined hormonal products in women who are comfortable eliminating their withdrawal period.4 While a dedicated, extended COC product is available in Canada, all currently available EE contraceptives (oral [monophasic or multiphasic], transdermal, vaginal) < 50 μg can be used in a continuous and/or extended regimen.4 The majority of Canadian women taking COCs, however, still follow the conventional 21/7 dosing regimen.