CONTRACEPTIVES
SHORT-ACTING HORMONAL METHODS
Short-acting hormonal contraceptives are such contraceptives which act on a hormonal (estrogen and/or progesterone) basis and are effective over a relatively short period (i.e. have to be taken repeatedly either daily, weekly or monthly). Hormonal contraceptives usually contain a combination of estrogens (such as estradiol) and progestins (synthetically produced forms of the naturally occurring hormone progesterone). But there are also progestin only contraceptive products (such as the "mini pill" or the contraceptive injection). Estrogen containing products bear a risk for blood clotting (thrombosis) and women with thrombotic issues may prefer progestin only contraceptives. Progestin only pills may also be the preferred choice for women with certain other counter-indications to estrogens, such as breastfeeding - as estrogen inhibits lactation. A major side effect in progestin only products is the risk for irregular menstrual bleeding, which typically gets better over time. Progestin, which is the main agent in any of these contraceptives (combination or not), works in several ways to prevent pregnancy (supported, in combination products, but low doses of estrogen).
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Firstly, it acts as a negative feedback on gonadotropin-releasing hormone (GnRH) in the hypothalamus, which in turn inhibits secretion of gonadotropins - follicle stimulating hormone (FSH) and luteinizing hormone (LH) - in the pituitary. Gonadotropins (specifically LH) are important female reproductive hormones responsible for ovulation. As a result, if there are higher levels of progestin in the body during the first half of the menstrual cycle, then the levels of LH and FSH spike will decrease at the mid-point of the menstrual cycle, thereby preventing ovulation from occurring. If ovulation is prohibited, no egg will be released from the ovaries, and so cannot be taken up by and fertilized in the fallopian tubes.
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Secondly, progesterone is responsible for preparing the endometrium (uterine lining) for embryonic implantation in the second half of the normal menstrual cycle (after ovulation). In the first half of the menstrual cycle (before ovulation), elevated estrogen levels have already caused endometrial cells to proliferate (endometrial thickening). Progesterone subsequently leads to an increased vascularization of the endometrium and increased nutrient transport to the endometrium. A thick endometrium is required so the egg - if it does get fertilized - can implant into and remain attached to the uterus for the duration of the pregnancy. Therefore, single high doses of progestin may actually increase fertility, because they contribute to endometrial thickening. However, it is believed that, if the progestin-estrogen ratio is held constantly high (meaning more progestin than estrogen is available over a longer period of time, even if overall doses are low, such as in hormonal birth control), this may lead to endometrial estrogen receptor inactivation which causes the endometrium to atrophy and get thinner, thereby making it impossible for an embryo to implant.
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Thirdly, higher levels of progesterone cause cervical mucus to thicken, which effectively blocks off the sperms' passage through the cervix into the uterus and the fallopian tubes, preventing it from joining and fertilizing the egg (even presuming one was released during ovulation).
Birth Control Pills
Oral birth control pills are possibly the most common short-acting hormonal contraceptive. They exist either as combination products (estrogen and progestin) or as progestin only contraceptives (the "mini pill"). Birth control pills are most effective when they are taken regularly every day around the same time. There are also different regimes for different birth control pills. For instance, the mini pill is often taken continuously every day throughout the entire month, thereby eliminating the monthly period in many women. Other pills are taken for about 21 days with an about 7 day pause at the end of each cycle, during which either no pill or an inactive form is taken. If the daily dose of a pill is omitted accidentally, it is best to continue taking the rest of the cycle as scheduled. To ensure maximum contraception, use of another contraceptive methods (such as condom or other barrier contraceptive) may be advisable. Most birth control pills offer protection about one week (7 days) after they are started, though some may need to be taken for an entire cycle (28 days) before becoming effective. Birth control offer theoretical efficiency rates of about 97-99% when taken correctly, although the risk of omitted taking may reduce their actual effectiveness to about 90%.
Skin Patch
The skin patch is a combination product and prescription medicine. It looks like a rectangular beige bandage and is attached to the skin, through which is releases both estrogen and progesterone into the blood. It needs to be changed weekly and costs up to $150 (without insurance). Its effectiveness is at around 90% when used correctly.
Vaginal Birth Control Ring
The vaginal ring is a combination product. It consists of supple plastic and contains both estrogen and progesterone to prevent pregnancy. Vaginal rings are prescription products. However, once they have been prescribed by a doctor and picked up in a pharmacy, they can be inserted and removed conveniently at home. After insertion into the vagina (with clean fingers, by squeezing the ring and pushing it up into a comfortable position), it releases the contraceptive hormones on a regular basis into the vagina, where they are taken up into the body through the vaginal lining. There are different products available on the market. For instance, NuvaRing (cost, depending on insurance coverage, around $200) is designed to last for about one cycle (one month), while Annovera (cost, depending on insurance coverage, around $2,000) lasts for up to an entire year (and can be taken out and cleaned for a 7-day window every cycle). Vaginal birth control rings have an effectiveness of about 99% if used correctly.
Contraceptive Injection
The contraceptive injection (shot) is a progestin only product. The injection is usually given in the arm or buttocks. It needs to be administered in a doctor's office and must be renewed every three (3) months. Depending on health insurance, it costs up to around $150. It is approximately 99% effective.
Emergency Contraceptives
Emergency contraceptives ("morning after pill") are hormone based contraceptives that can prevent pregnancy if they are taken within 72 hours after unprotected sex has occurred. There are two types of emergency contraceptives. Progestin-based products (levonorgestrel, used in lowed dosages in many conventional birth control pills) - which are over the counter products - and selective progesterone-receptor modulators (ulipristal) - which are prescription medicines, and which are believed to be more effective than levonorgestrel. Even though these products decrease he risk of an unwanted pregnancy by abut 75-90%, if ovulation or fertilization have already occurred, no emergency contraceptive can be effective.