Contraception is the prevention of pregnancy following sexual intercourse by inhibiting sperm from reaching a mature ovum (i.e., methods that act as barriers or prevent ovulation) or by preventing a fertilized ovum from implanting in the endometrium (i.e., mechanisms that create an unfavorable uterine environment).
Method failure (perfect-use failure) is a failure inherent to the proper use of the contraceptive alone.
User failure (typical use failure) takes into account the user’s ability to follow directions correctly and consistently.
The Menstrual Cycle :
- The median length of the menstrual cycle is 28 days (range 21 to 40).
- The first day of menses is day 1 of the follicular phase.
- Ovulation usually occurs on day 14 of the menstrual cycle.
- After ovulation, the luteal phase lasts until the beginning of the next cycle.
- Epinephrine and norepinephrine stimulate the hypothalamus to secrete gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to secrete bursts of gonadotropins, follicle-stimulating hormone (FHS) and luteinizing hormone (LH).
- In the follicular phase, FSH causes recruitment of a small group of follicles for continued growth. Between 5 and 7 days, one of these becomes the dominant follicle, which later ruptures to release the oocyte. The dominant follicle develops increasing amounts of estradiol and inhibin, which cause a negative feedback on the secretion of GnRH and FSH, causing atresia of the remaining follicles recruited earlier.
- The dominant follicle continues to grow and synthesizes estradiol, progesterone, and androgen. Estradiol stops the menstrual flow from the previous cycle, thickens the endometrial lining, and produces thin, watery cervical mucus. FSH regulates aromatase enzymes that induce conversion of androgens to estrogens in the follicle.
- The pituitary releases a mid-cycle LH surge which stimulates the final stages of follicular maturation and ovulation, which occurs 24 to 36 hours after the estradiol peak and 10 to 16 hours after the LH peak.
- The LH surge occurring 28 to 32 hours before a follicle ruptures is the most clinically useful predictor of approaching ovulation. Conception is most successful when intercourse takes place from 2 days before ovulation to the day of ovulation.
- After ovulation, the remaining luteinized follicles become the corpus luteum, which synthesizes androgen, estrogen, and progesterone.
- If pregnancy occurs, human chorionic gonadotropin (hCG) prevents regression of the corpus luteum and stimulates continued production of estrogen and progesterone. If pregnancy does not occur, the corpus luteum degenerates, and progesterone declines. As progesterone levels decline, menstruation occurs.
Treatment (Contraception) :
The abstinence (rhythm) method is not well accepted as it is associated with relatively high pregnancy rates and necessitates avoidance of intercourse for several days in each cycle.
- Barrier methods, including the diaphragm, cervical cap, sponge, condom, and spermicides, can reduce the rate of sexually transmitted disease (STD) transmission.
- The effectiveness of the diaphragm depends on its function as a barrier and on the spermicidal cream or jelly placed in the diaphragm before insertion.
- The Prentif cervical cap, smaller and less messy than the diaphragm, fits over the cervix like a thimble. It is filled one-third full with spermicide prior to insertion. Women should not wear the cap for longer than 48 hours to reduce the risk of toxic shock syndrome.
- Most condoms made in the United States are latex rubber, which is impermeable to viruses, but about 5% are made from lamb intestine, which is not. When used with another barrier method, the effectiveness of condoms approaches 95%. Mineral oil-based lotions, lubricants, or vaginal drug formulations (e.g., Cleocin vaginal cream, Premarin vaginal cream, Vagistat 1, Femstat, and Monistat Vaginal suppositories) can decrease barrier strength of latex by 90% in 60 seconds.
- The female condom (Reality) covers the labia as well as the cervix, thus it may be more effective than the male condom in preventing transmission of diseases such as herpes. However, the pregnancy rate is reported to be 26% per year, based on a 6-month follow-up study of 200 women.
Pharmacologic Therapy :
Spermicides, most of which contain nonoxynol-9, are surfactants that destroy sperm cell walls. They offer some protection against STDs and cervical cancer. Tablets and suppositories require 10 to 30 minutes to dissolve. Additional spermicide must be used each time intercourse is repeated.
Spermicide-implanted Barrier Techniques
The vaginal contraceptive sponge (Today) contains 1 g of nonoxynol-9 and provides protection for 24 hours. After intercourse, the sponge must be left in place for at least 6 hours before removal. It is now being reviewed by the Food and Drug Administration (FDA) for re-release in the United States.
Oral Contraceptives (OCs)
- OCs contain either a combination of synthetic estrogen and synthetic progestin or a progestin alone.
- Estrogens suppress FSH and thus prevents development of a dominant follicle. They also stabilize the endometrial lining and potentiate the action of the progestin.
- Progestins suppress the LH surge and thus block ovulation. They also thicken cervical mucus and causes the endometrium to atrophy.
- The low dose combination OCs contain approximately one third to one fourth the estrogen and one tenth the progestin dose that was in the earlier pills.
- Combination multiphasic (biphasic and triphasic) formulations have further lowered the total monthly hormonal dose without clearly demonstrating clinical advantage.
- The progestin-only (28 days of active hormone per cycle) are also available, and they contain even lower doses of progestin than in the combination OCs. They are less effective than the combination OCs with typical use and are usually reserved for women who must avoid estrogen.