Contraception
The risk of pregnancy without contraception is 2–4% for each unprotected
act of intercourse. In 100 women using no contraception, 85 pregnancies occur
per year. Approximately half of all pregnancies in the developed world are
unplanned and many of these women report using some form of reversible birth
control at the time they became pregnant. Only absolute abstinence completely
prevents pregnancy. While no form of contraception is perfect in sexually
active women, helping patients to choose a contraceptive method that they are
able to use consistently and correctly can decrease unintended pregnancy (Fig.
25.1). With perfect use, oral contraceptives (OC) are nearly as effective as
long-acting reversible contraceptives (LARC), such as the intrauterine device
(IUD), progesterone intramuscular injection and progesterone implants. However,
with typical use, LARC methods are approximately 10 times more effective.
“Natural” family planning
Natural family planning or
fertility awareness aims to avoid conception by abstention from intercourse
during the woman’s fertile period. It makes use of a calendar and some
indicator of ovulation (basal body temperature measurements, cervical mucus
characteristics or commercial ovulation prediction kits). Intercourse is
avoided during the so-called fertile period at ovulation and for several days
before and after. Natural family planning requires a highly motivated couple,
regular menstrual cycles and the willingness to tolerate a failure rate of up
to 25%. The method has no medical side effects and is accepted by virtually all
religions.
Barrier methods
There are three general
categories of barrier contraception: condom, diaphragm and cervical cap. All
work by preventing spermatozoa from entering the woman’s uterus and fertilizing
an egg. Barrier methods are good choices for individuals who want to limit
contraceptive efficacy to a particular sexual episode. They are readily
reversible and can be used in conjunction with the timing methods associated
with natural family planning. The most serious side effects of barrier methods
occur in individuals with an unknown latex allergy.
Condoms that fit over the
penis are more widely available than condoms that fit inside the vagina (the
female condom). Male condoms may be made from latex rubber, polyurethane or
animal intestines; each provides a different “feel” or sensitivity for the man
during intercourse. Female condoms are typically made of polyurethane. Intact
condoms stop sperm and infectious agents from entering the vagina and so can
prevent transmission of HIV and other sexually transmitted diseases. They must
be carefully removed after ejaculation to avoid spilling semen from the condom
into the vagina. The failure rates of condoms are 3–6% with perfect use and 15%
with typical use. The diaphragm is a soft latex or plastic dome that
fits inside the vagina and covers the cervix. Because some sperm may be able to
bypass the diaphragm and gain access to the uterus, spermicide is placed in the
dome of the diaphragm. Diaphragms are individually fitted by a clinician and
require some training for proper insertion and removal. A diaphragm should be
left in place for 6–8 h after inter course, and additional spermicide placed
into the vagina if more episodes of intercourse occur before it is removed.
Diaphragms partially protect against HIV and other sexually transmitted
diseases. Some women develop bladder or vaginal infections during diaphragm
use. The failure rate of a properly fitted diaphragm with perfect use is about 6%; it rises to 15% with typical use.
Cervical caps are similar
to, but smaller than, the diaphragm. They are individually fitted to tightly
cover the cervix. Failure rates are similar to those of the diaphragm. Cervical
caps are not widely available.
Spermicides
These are chemicals that kill
sperm by disrupting their outer cell membranes. The most commonly used are
nonoxynol-9 and octoxynol-9. Spermicides are available suspended in one of
three vehicles: foam, jelly or wax suppositories. Spermacides are recommended
for use with a barrier method, because the failure rate of spermicide used
alone is up to 30%. There are few absolute contraindications to their use. They
have an unpleasant taste and can cause an allergy in some users. Spermicide use may
cause inflammation of the female genital tract and has been associated with an
increase in the transmission of sexually transmitted infections, including HIV.
Intrauterine devices
The IUD is a small T-shaped
device, placed into the uterine cavity and attached to a monofilament thread
that hangs into the vagina, allowing the user to confirm that it remains in
place. The modern IUD provides safe, long-acting, highly effective and rapidly
reversible contraception with few side effects.
The precise contraceptive mechanism of the IUD is not known,
but it is thought to work by preventing fertilization as well as causing the
endometrium to be inhospitable for implantation. The 10–12 year copper IUD
produces a local inflammatory response in the endometrium and excess
prostaglandin production. The copper ion competitively inhibits a number of
zinc-requiring processes in sperm activation and endometrium/ embryo signaling.
The 3- and 5+-year progestin-releasing IUDs thickens cervical mucus, creating a
barrier to sperm penetration into the upper genital tract. Additionally, the
progestin disrupts the normal proliferative- to-secretory sequence of
endometrial maturation.
Historically, IUDs, such as the
Dalkon Shield, were associated with increased risk for medical complications
and reproductive damage among users who were infected with sexually transmitted
pathogens. This increased risk was likely due to the braided IUD tail, which
allowed bacteria to ascend into the upper genital tract. The monofilament
string, used on all modern IUDs, does not have this risk. In women at high risk
for sexually transmitted infections (STIs), screening should be performed prior
to IUD insertion. Women should be advised to use a barrier method for
prevention of HIV and other STIs. Side effects of the copper IUD include
increased menstrual bleeding, iron-deficiency anemia and dysmenorrhea. The
progestin IUD reduces menstrual flow and may be used to treat menorrhagia and
adenomyosis. The IUD is highly effective, with a failure rate <1% per year.
If pregnancy occurs, it is more likely to be ectopic in location. However,
compared with women using no form of contraception, women with IUDs still have a reduced risk of
ectopic pregnancy.
Hormonal contraception
Combination oral contraceptive pills (often called OCPs) are the most
widely used form of hormonal contraception. They include a synthetic estrogen (ethinyl estradiol or mestranol)
combined with a variety of synthetic progestins and are typically taken orally
for 21 consecutive days of every 28 and allow monthly withdrawal bleeding. The
progestin component of combination OCPs varies in its activity on progesterone
receptors, androgen receptors and mineralocorticoid receptors. The estrogen and
progestin dosages in monthly combination OCPs may be constant over the 21 days
or may be sequentially modulated (phased or triphasic pills). Some newer
combination oral contraceptive regimens provide continuous rather than monthly
exogenous hormone cycles, often allowing endometrial sloughing only 3-4 times
per year. Combination OCPs prevent pregnancy by multiple mechanisms, including
inhibition of ovulation, thickening of cervical mucus to prevent sperm
transport and alteration of the uterine lining to block implantation.
OCPs have benefits beyond
pregnancy prevention, including decreased risk of pelvic inflammatory disease
(PID), benign breast disease, anemia and endometrial and ovarian cancer. They
are not totally risk free, however, and are associated with increased risk of
thromboembolic disease, nonthrombotic stroke and gallbladder disease. Women
over 35 who smoke should not use combination OCPs. Failure rates are <1%
with perfect use and about 8% with typical use. To be effective, OCPs must be
taken in the correct order on a daily basis.
Combinations of estrogen and
progestin are also available for contraception in nonoral formulations. These
include transdermal patches, injections and vaginal rings. All have efficacy
similar to combination OCPs, and may have reduced metabolic side effect
profiles.
Progestin-only contraceptives can be administered orally, by intramuscular injection or as a subdermal
implant. All work by thickening cervical mucus and altering the endometrial
lining of the uterus. The oral form of the progestin-only contraceptive, often
called the mini- pill, is useful in women with contraindications to estrogen
such as breastfeeding or high thrombotic risk. With perfect use, the mini-pill
has a failure rate comparable with OCPs. However, the half-life of the
mini-pill is short, with nearly undetectable plasma levels at 24 h. Thus, to
maximize effectiveness, the mini-pill requires precise compliance with all 28
active pills taken at the same time daily.
Depo-medroxyprogesterone acetate
(DMPA) is a progestin contraceptive given as an intramuscular injection every
12–14 weeks. Common side effects include irregular bleeding, particularly in
the first 6 months of use, and weight gain. Because of the length of action of
DMPA, side effects may persist until the medication is cleared and return to
fertility may be delayed.
The original six-capsule
subdermal levonorgestrel progestin implant (Norplant) has been replaced with an
equivalent two-capsule system (Jadelle, 5 years of use), and a single capsule
subdermal etonorgestrel implant (Implanon, 3 years of use). Insertion and
removal are generally quick and uncomplicated, but must be performed by a
trained clinician. Side effects include irregularly irregular vaginal bleeding.
Hormonal emergency contraception can be effective in preventing pregnancy if taken within the given time
interval after unprotected intercourse or a contraceptive failure. Plan B,
consisting of 1.5 mg levonorgestral, prevents pregnancy using the same
mechanisms as other progestin contraceptives if taken within 120 h of exposure.
Combination estrogen progestin emergency
contraception may also
be used up to 120 h following exposure; however, the combined hormonal
regimen has more side effects and a lower effectiveness than the progestin-only
regimen. The copper IUD may also be used for emergency contraception up to 5
days after unprotected intercourse.
Sterilization
Sterilization of both men and
women are surgical methods of permanent contraception. Sterilization prevents
the gametes from reaching the point of fertilization.
In women, sterilization is
commonly performed by laparoscopic tubal ligation. Tubal ligation
interrupts the fallopian tubes and may involve the use of tying, blockade,
cautery, partial excision or banding. Ten-year cumulative failure rates for
female sterilization are 0.75– 3.5%, depending upon the method. If a pregnancy
does occur after tubal ligation, up to 50% are in an ectopic (tubal) location
because of the blockage of the fallopian tube. Transcervical sterilization involves
placement of micro-inserts into the fallopian tubes using a hysteroscope. This
method requires no incision and can be performed in a doctor’s office.
Disadvantages include the need to wait 3 months for tubal occlusion to occur
and confirmation of occlusion using a radiographic dye test called a
hysterosalpingogram. Failure rates appear similar to laparoscopic methods.
The sterilization procedure used
in men is called a vasectomy. It involves bilateral interruption of the
vas deferens as they leave the testes in the scrotum. Surgical methods for
interruption include partial excision, cautery or tying. Vasectomy is typically
100% effective but requires a 3-month waiting period and multiple postprocedure
ejaculations to clear the vas deferens of previously produced sperm.
