28
1090
In a society such as ours, where
many women opt for professional
careers or work for economic reasons,
contraception
(
contra
5
against,
cept
5
taking), commonly called
birth control
,
is often seen as a necessity.
The key to birth control is
dependability
. As the red arrows in
the accompanying flowchart show, the
birth control techniques currently available
have many sites of action for
blocking
reproduction
. Generally speaking,
birth control methods can be categorized
into three groups based on how each
prevents pregnancy—behavioral methods,
barrier methods, or hormonal methods.
Let’s examine a few of them more closely.
Behavioral methods
(coitus
interruptus, the rhythm method, and
abstinence) consist of altering behavior
to prevent pregnancy.
Coitus interruptus
,
or withdrawal of the penis just before
ejaculation, is unreliable because control
of ejaculation is never ensured.
Rhythm
or
temporary abstinence
methods
involve avoiding intercourse
during periods of ovulation or fertility.
This may be accomplished by recording
daily basal body temperatures (body
temperature drops slightly immediately
prior to ovulation and then rises slightly
after ovulation). This technique requires
accurate record keeping for several cycles
before it can be used with confidence, but
has a high success rate for those willing to
take the time necessary. With a failure rate
of 10–20%, it is obvious that some people
are willing and some are not.
Barrier methods
include diaphragms,
cervical caps, male and female condoms,
and spermicides. These techniques prevent
the sperm and egg from meeting and
implanting. They are quite effective,
especially when used in combination—for
example, condoms and spermicides. But
many people avoid them because they
can reduce the spontaneity of sexual
encounters.
Hormonal methods
include a
broad variety of hormone-containing
contraceptive products (the pill, IUD,
patches, vaginal ring, and implanted or
injected agents). These methods are highly
effective, with a failure rate of less than
1%, and have a low risk of adverse effects
in most women.
The most-used contraceptive product in
the United States is the
oral contraceptive
pill
(
OCP
) or simply “the pill,” first
marketed in 1960. Supplied in 28-tablet
packets, the first 20 or 21 tablets contain
minute amounts of estrogens and
progestins (progesterone-like hormones)
which are taken daily; the hormones
contained may be of fixed or of varying
combinations. The last seven tablets are
hormone free—are placebos or are iron
pills. The pill tricks the hypothalamic-
pituitary-gonadal axis and “lulls it to
sleep,” because the relatively constant
blood levels of ovarian hormones make
it appear that the woman is pregnant
(both estrogen and progesterone are
produced throughout pregnancy). Ovarian
follicles do not develop, ovulation ceases,
and menstrual flow is much reduced.
Contraception: To Be or Not To Be
However, since hormonal balance is one
of the most precisely controlled body
functions, some women cannot tolerate
these changes—they become nauseated
and/or hypertensive. The pill has adverse
cardiovascular effects in a small number
of users and there is still debate about
whether it increases the risk of uterine,
ovarian, or (particularly) breast cancer.
Presently, well over 50 million women use
the pill.
Other delivery methods using the
combination hormone approach include
two slow-release products—a flexible
ring that is inserted into the vagina,
and a transdermal (skin) patch. Failure
rates and side effects of the vaginal ring
A
C L O S E R
LOOK
Intrauterine
device (IUD);
progestin only
(minipill, implant,
or injection)
Morning-
after pill (MAP)
Implantation of blastocyst
in properly prepared endometrium
Union of sperm and ovum
Meeting of sperm and oocyte
in uterine tube
Sperm move
through the
female’s
reproductive
tract
Transport down
the uterine tube
Spermicides,
diaphragm,
cervical cap,
vaginal pouch,
progestin only
(implant or
injection)
Tubal ligation
Capture of the
oocyte by the
uterine tube
Sperm deposited
in the vagina
Coitus
interruptus
(high failure
rate)
Abstinence
Abstinence
Female
condom
Condom
Vasectomy
Technique
Production of
viable sperm
Male
Event
Transport down
the
male duct
system
Event
Production of
primary oocytes
Female
Technique
Ovulation
Combination birth
control pill, patch,
monthly injection,
or vaginal ring
Mechanisms of contraception.
Techniques or products that interfere with events from production
of gametes to implantation are indicated by red arrows at the site of interference and act to prevent
the next step from occurring.
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