**8.2 Types**

There are various types of emergency contraceptive pills (ECPs), including:


In Europe, UPA-ECPs have been available since 2009; subsequently, they received approval in the U.S. from the FDA in 2010 for use as an emergency contraceptive. They are now available in more than 50 countries [78].

#### **8.3 Mechanism of action**

The risk of pregnancy after an episode of UPSI is difficult to estimate because it depends on a number of factors, including the fertility of both partners, the timing and number of acts of UPSI, cycle length and variability, and whether contraception has been used incorrectly or not at all. Pregnancy is extremely unlikely to occur as a result of UPSI in the first 3 days of a woman's natural menstrual cycle [141]. However, pregnancy is theoretically possible after UPSI on most days of the cycle. A woman's fertile period is considered to be the 6 consecutive days ending with, and including, the day of ovulation.

Sperm are viable in the female genital tract for about 5 days after UPSI [141]. If ovulation occurs within those 5 days, fertilization could take place and the woman is at risk of pregnancy. A judicial review concluded that pregnancy begins at implantation [176]. It is therefore currently accepted that any emergency contraception intervention must act either to prevent fertilization or to prevent implantation, rather than to disrupt established implantation. According to available data, the shortest time from ovulation to implantation is 6 days, although over 80% of pregnancies implant 8–10 days after ovulation [177].

LNG-ECPs inhibit ovulation, delaying or preventing follicular rupture and causing luteal dysfunction. If taken prior to the start of the LH surge, LNG inhibits ovulation for the next 5 days, until sperm from the UPSI for which it was taken are no longer viable [178]. In the late follicular phase, however, LNG-ECPs become ineffective [179]. Although post-ovulation effects of LNG-ECP have been suggested, subsequent studies have not shown a significant effect when administered after ovulation [180]. *In vitro*, LNG-ECPs have not been found to impair endometrial receptivity or the attachment of human embryos [181].

UPA is a selective progesterone receptor modulator that acts by delaying ovulation for at least 5 days, until sperm from the UPSI are no longer viable. Unlike LNG-ECPs, UPA-ECPs delay ovulation even after the start of the LH surge [179]. However, UPA-ECPs cannot inhibit ovulation at or after the LH peak. Moreover, UPA-ECPs have not been demonstrated to be as effective as other ECPs when administered after ovulation. Li et al. found a significant difference between observed and expected pregnancy rates for women who received UPA-ECPs prior to ovulation, but not for women who received UPA-ECPs after ovulation [182].

Despite this, various theoretical mechanisms of action have been suggested for a post-ovulation effect of UPA, including delayed endometrial maturation; however, the clinical relevance of this in terms of its contribution to preventing pregnancy is unclear [183]. *In vitro*, UPA-ECPs have not been found to inhibit endometrial receptivity, prevent human embryo attachment to the endometrium, or affect sperm function [184, 185].

### **8.4 Effectiveness**

The overall effectiveness of ECPs is difficult to ascertain. Most studies report the pregnancy rate after use of various types of ECPs as a percentage of the number of women who used ECPs; however, a significant number of these women would not

have become pregnant in any case. Studies assessing the effectiveness of ECPs in preventing pregnancy depend, therefore, on an estimation of the number of pregnancies that would have occurred without the emergency contraception intervention.

UPA-ECPs have been demonstrated to be effective when taken up to 120 h after an episode of UPSI, with no significant reduction in effectiveness observed with increasing time until this point [186, 187]. The overall pregnancy rate after taking UPA-ECPs has been reported to be 1–2% [186, 187].

Studies have reported the overall pregnancy rate among women taking LNG-ECPs within 72 h of an episode of UPSI to be 0.6–2.6% [186, 188]. However, in several of these studies, the LNG-ECPs were taken at any time of the cycle; thus, UPSI may or may not have occurred when the women were at risk of pregnancy. Two large RCTs comparing LNG-ECPs to other ECP regimens estimated the number of pregnancies that would have occurred without the intervention and compared this with the actual number of pregnancies observed [188]. The percentage of pregnancies prevented by LNG-ECPs, when taken within 72 h of a single episode of UPSI, was estimated to be about 85%.

### **8.5 Advantages**

Overall, ECPs can be used by women of any age, including adolescents and women with HIV. They do not cause abortion and do not prevent or affect implantation. In addition, they do not cause birth defects if pregnancy occurs. ECPs are considered safe for women's health and do not cause infertility. Oral ECPs can be used more than once in a women's cycle and a woman can take ECPs when needed without first seeing a health care provider. No procedures or tests are needed before taking ECPs, apart from a pregnancy test if indicated [78].

#### **8.6 Disadvantages**

Women may have cultural or religious reasons for avoiding a method of emergency contraception that could have its effect after fertilization [189]. It is therefore important that a client who raises concerns about the mechanism of action of any emergency contraception intervention is given sufficient information about what is known and what is uncertain.

#### *8.6.1 Side-effects*

Nausea, abdominal pain, fatigue, headaches, breast tenderness, dizziness, and vomiting are commonly reported side-effects of ECPs. Some users also report changes in bleeding patterns after ECP administration, including slight irregular bleeding for 1–2 days or monthly bleeding that starts earlier or later than expected in the first several days after taking ECPs. However, irregular bleeding due to ECPs will typically stop without additional treatment [78].

#### *8.6.2 Risks*

A Cochrane review identified only 5 cases of ectopic pregnancy among over 55,000 oral ECP users [190]. Frequent repeated use of ECPs may be harmful for women with cardiovascular diseases, migraine, or severe liver disease [78].

*Perspective Chapter: Modern Birth Control Methods DOI: http://dx.doi.org/10.5772/intechopen.103858*
