The Reproductive. S
J
asonandBonniehave been unsuccessful in starting a
family and have decided to consult a fertility specialist
to determine what is wrong. One out of every six couples
experience
infertility
, defined as being unable to get
pregnant for at least 12 consecutive months. There are
a number of possible causes: About 40% of the cases are
related to an issue with the male; 40% are related to an
issue with the female; and the remaining 20% are due to a
combination of male and female issues.
Infertility in the male is often associated with low
sperm counts or high numbers of defective sperm. This
can be due to harmful environmental chemicals (cigarette
smoke, lead, pesticides, and so on), high testicular tem-
peratures (due to tight clothing or certain occupations),
or abnormal hormone levels. In the female, the most
common causes are related to a lack of egg release and
abnormal pathways for the sperm and egg. Abnormal hor-
mone levels and infections (especially sexually transmitted
diseases) are most often involved. For both the males and
females, fertility rates continue to decrease after age 25.
For some couples, the problem lies in compatibility be-
tween the male and female, even though both are “func-
tioning normally.”
Many infertile couples turn to reproductive special-
ists and assisted reproductive technologies to improve
their chances of a successful pregnancy. In one technique,
in v itr o
fertilization (IVF)
, the woman is given drugs to
enhance her egg production, and the eggs are harvested.
Following injection with sperm in the laboratory, the result-
ing embryos are allowed to develop briefly and are then
transferred into the woman’s uterus. If all goes well, she
will deliver a healthy baby. Often, more than one embryo is
transferred for better chances of success; if more than one
implants, multiple births may occur. This technology has
enabled many infertile couples to have children. However,
the fact that it can also result in multiple births has become
controversial in recent cases and has led to medical board
review of IVF candidate selection.
In this chapter, we examine the male and female
reproductive systems, as well as the growth and develop-
ment of a new human being from fertilization to birth.
468
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