*2.1.1 Estrogen*

The majority of combined oral contraceptives (COCs)—as well as the combined transdermal patch and combined vaginal ring—contain between 20 and 35 μg of ethinylestradiol (EE), a synthetic form of estrogen. Current 'low-dose' COCs were developed to reduce the health risks associated with the high estrogen content of COCs used in the 1960s and 1970s [13]. Low-dose COCs (i.e., formulations containing <50 μg of EE) are a safe and reliable contraceptive option for the vast majority of women [14, 15].

## *2.1.2 Progestogens*

Progestogens are synthetic steroids designed to have some of the properties of progesterone. The synthetic progestogen component of CHC allows for convenient dosing intervals, potent suppression of ovulation, and prevents overproliferation of the endometrium in response to estrogen. Newer progestogens were developed to have fewer androgenic and glucocorticoid effects; some are anti-androgenic and have potentially favorable anti-mineralocorticoid effects [16]. However, different progestogens can modify the effect of EE on hepatic clotting factors in different ways; for example, forms of CHC which contain certain newer progestogens in combination with EE appear to be associated with a greater risk of venous thromboembolism (VTE) compared to COCs containing other progestogens [17–21].

The different progestogens included in CHC are sometimes grouped by 'generation' as below, according to the time they were first marketed as constituents of COCs: *Perspective Chapter: Modern Birth Control Methods DOI: http://dx.doi.org/10.5772/intechopen.103858*


### **2.2 Types**

There are currently two types of CHC regimens offered: standard hormonal regimens or tailored/combined regimens.

### *2.2.1 Standard regimens*

The majority of COCs are designed to be taken on a 28-day cycle, with 21 consecutive daily active pills followed by a 7-day hormone-free interval prior to starting the next packet of pills. The first 7 pills inhibit ovulation and the remaining 14 pills maintain anovulation.

For combined transdermal patches, 1 patch is applied to the skin and worn for 7 days to suppress ovulation. Thereafter the patch is replaced on a weekly basis for 2 further weeks. The fourth week is patch-free to allow a withdrawal bleed. A new patch is then applied after 7 patch-free days [23].

For combined vaginal rings, 1 ring is inserted into the vagina and left in place continuously for 21 days. After a ring-free interval of 7 days to induce a withdrawal bleed, a new ring is inserted [24].

The majority of COC products are monophasic; that is, all pills in the packet contain the same dose of estrogen and progestogen. Multiphasic (variable dose) COCs are also available in which the dose of either or both steroid hormones varies during the pill cycle. Evidence is inadequate to establish whether multiphasic COCs differ significantly from monophasic COCs in terms of bleeding patterns, side-effects, discontinuation rates, or effectiveness in preventing pregnancy [25–27]. As existing evidence suggests there is no particular advantage to multiphasic preparations, it is recommended that monophasic COCs should be used as a first-line intervention.

#### *2.2.2 Tailored regimens*

Tailored CHC regimens include:


In continuous or extended CHC regimens, the contraception is taken for more than 21 consecutive days without a hormone-free interval. Such regimens have the potential advantage of eliminating or reducing the frequency of withdrawal bleeding and associated symptoms; the bleeding pattern is, however, unpredictable.

Less frequent hormone-free intervals could also reduce the risk of escape ovulation and, potentially, contraceptive failure [28–31]. A shortened hormone-free interval, offering more continuous ovarian suppression, could also reduce the risk of escape ovulation, particularly if contraceptive use is imperfect around the hormone-free interval. A shortened hormone-free interval can be taken either after every 21 days of active CHC use or incorporated into an extended regimen.
