Combined Hormonal Contraception
Background
Combined Hormonal Contraception (CHC) has been around for nearly 60 years and used by millions of women worldwide. It is a highly effective method of contraception, 99% effective if taken correctly, though in practice typical pregnancy rate is 9% in first year of use. In the UK, it is usually prescribed as a tablet (combined oral contraception, COC) containing </= 35ug synthetic estrogen ethinylestradiol combined with a synthetic progestogen. It is also available in the form of a patch or a ring. The following guidance refers to the use of low dose COC (</=35ug ethinylestradiol).
Action
COC prevents ovulation by acting on the hypothalamic-pituitary-ovarian axis through its suppression of LH and FSH. The progestogen may also affect cervical mucus, endometrial proliferation and tubal motility.
Types
Most COC in regular use comprise of </= 35ug ethinylestradiol and a progestogen. There are several types of progestogens available, broadly divided into older and newer generation progestogens. The older progestogens include norethisterone and levonorgestrel; the newer progestogens include desogestrel, gestodene, norgestimate, drospirenone, dienogest, and nomegestrol acetate. The newer progestogens, designed to have less androgenic and glucocorticoid effects, are associated with a greater risk of VTE (venous thromboembolic disease) and are therefore not considered first-line choice.
While the majority of COC are monophasic (dose of estrogen and progestogen is constant throughout usage), some are multiphasic (variable dosing throughout the pill cycle). Due to limited trials, there is no existing evidence to suggest any particular advantage of multiphasic COC compared with monophasic. FSRH recommends monophasic as first-line.
COC containing estradiol, a structurally identical to human estrogen, is available, though there is limited evidence on its safety compared to COC with ethinylestradiol.
Non-oral CHC include the combined transdermal patch (CTP) and combined vaginal ring (CVR). The CTP releases an average of 33.9 ug EE and 203ug or norelgestromin/24h, whereas the CVR releases 15ug EE and 120ug etonogestrel/24hours. Both are options for patients wishing to remain on CHC (e.g. bowel conditions).