Reproduction
639
to progesterone receptors in the uterus but does not activate
them. Antagonism of progesterone’s effects causes the endo-
metrium to erode and the contractions of the fallopian tubes
and myometrium to increase. RU 486 can also be used later in
pregnancy as an abortifacient.
The
rhythm method
uses abstention from sexual inter-
course near the time of ovulation. Unfortunately, it is diffi cult
to time ovulation precisely, even with laboratory techniques.
For example, the small rise in body temperature or change in
vaginal epithelium, all of which are indicators of ovulation,
occur only
after
ovulation. This combined with the marked
variability of the time of ovulation in many women—from day
5 to day 15 of the cycle—explains why the rhythm method
has a high failure rate.
There are still no effective chemical agents for male con-
traception. One potential approach is to decrease gonadotro-
pin levels, which would decrease spermatogenesis. Testosterone
would then have to be given to maintain libido.
Infertility
Approximately 12 percent of men and women of reproductive
age in the United States are infertile. The numbers of infertile
men and women are approximately equal until about age 30,
after which infertility becomes more prevalent in women. In
many cases, infertility can be successfully treated with drugs,
artifi cial insemination, or corrective surgery.
When the cause of infertility cannot be treated, it can
sometimes be circumvented in women by the technique of
in vitro fertilization
.
First, the woman is injected with drugs
that stimulate multiple egg production. Immediately before
ovulation, at least one egg is then removed from the ovary via
a needle inserted into the ovary through the top of the vagina
or the lower abdominal wall. The egg is placed in a dish for
several days with sperm. After the fertilized egg has developed
into a cluster of two to eight cells, it is then transferred to the
woman’s uterus. The success rate of this procedure, when one
egg is transferred, is only about 15 to 20 percent.
Menopause
Around the age of 50, on the average, menstrual cycles become
less regular. Ultimately they cease entirely, and this cessation is
known as
menopause.
The phase of life beginning with men-
strual irregularity is termed
perimenopause.
It involves many
physical and emotional changes accompanying the cessation of
reproductive function.
Menopause and the irregular function leading to it are
caused primarily by ovarian failure. The ovaries lose their abil-
ity to respond to the gonadotropins, mainly because most, if
not all, ovarian follicles and eggs have disappeared by this time
through atresia. The hypothalamus and anterior pituitary con-
tinue to function relatively normally as demonstrated by the
fact that the gonadotropins are secreted in greater amounts.
The main reason for this is that the decreased plasma estro-
gen and inhibin do not exert as much negative feedback on
gonadotropin secretion.
Table 17–12
Some Forms of Contraception
Method
First Year Failure Rate*
Physiological Mechanism of Effectiveness
Barrier Methods
Condoms (
and
)
Diaphragm/cervical cap (
)
12%
Prevent sperm from entering uterus
Spermicides
(
)
20%
Kill sperm in the vagina (after insemination)
Sterilization
Vasectomy (
)
Tubal ligation (
)
<0.5%
Prevents sperm from becoming part of seminal fl
uid
Prevents sperm from reaching egg
Intrauterine device (IUD)
(
)
3%
Prevents implantation of blastocyst
Estrogens and/or Progestins
Oral contraceptive pill (
)
Emergency oral contraception (
)
Injectable or implantable progestins (
)
Transdermal (skin patch) (
)
Vaginal ring (
)
3%
1%
<0.5%
<1%
<1%
Prevent ovulation by suppressing LH surge (negative
feedback); thicken cervical mucus (prevents sperm
from entering uterus); alter endometrium to prevent
implantation of blastocyst
*From Hall, J. E., Infertility and Fertility Control,
Harrison’s Principles of Internal Medicine,
McGraw-Hill, 2004. Rosen, M., and Cedars, M. I. Female Reproductive Endocrinology and Infertility.
Basic
and Clinical Endocrinology,
7th ed., McGraw-Hill, 2004; ACOG Practice Bulletin. Emergency Contraception.
Obstet. Gynecol.
2005, 106:1443–52. See also www.fda.gov. Failure rate assumes proper and
consistent use.
Notes
Spermicides are often used in combination with diaphragm/cervical cap and condoms.
Only condoms are effective in preventing sexually transmitted diseases.
Rhythm method (abstinence around time of ovulation) and coitus interruptus (withdrawal) are not listed because they are not reliable.
Only total abstinence is 100% effective in preventing pregnancy.
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