HUMAN BIOLOGY

318 Chapter 16

in vitro fertilization
Fertilization that occurs
when oocytes and sperm
are placed in a prepared
laboratory dish.

options for Coping with infertility

effects, including the fertilization of several eggs at once.

The result is a high-risk pregnancy that can result in babies

with neurological and other problems.

assisted reproductive technologies include

artificial insemination and ivF

Artificial insemination was one of the first methods of

assisted reproductive technology, or ART. In this approach,

semen is placed into a woman’s vagina or uterus, usually by

syringe, around the time she is ovulating. This procedure

may be chosen when a woman’s partner has a low sperm

count, because his sperm can be con centrated prior to the

procedure. In artificial insemination by donor (AID), a sperm

bank provides sperm from an anonymous donor. AID pro-

duces about 20,000 babies in the United States every year.

In vitro fertilization (IVF) is literally fertilization “in

glass.” If a couple’s sperm and oocytes are normal, they can

be used. Otherwise, variations of the technol ogy are avail-

able that use sperm, oocytes, or both, from donors (Figure

16.14B). Sperm and oocytes are placed in a glass laboratory

dish in a solution that simulates the fluid in oviducts. If fer-

tilization takes place, about 12 hours later zygotes (fertilized

eggs in the first stage of development) are transferred to a

chemical solution that will support further development.

Two to four days later, one or more embryos are trans-

ferred to the woman’s uterus. An embryo implants in about

20 percent of cases. In vitro fertilization often produces more

embryos than can be used in a given procedure. The fate of

unused embryos (which are stored frozen) has prompted

ethical debates, such as whether such embryos should be

used as a source of embryonic stem cells (Chapter 4).

n In the United States, about one in every seven couples is

unable to conceive a child after a year of trying.

n    Link to Hormones from the hypothalamus and pituitary 15.3

About 20 percent of the time it’s not possible to determine

the cause of infertility. In general, infertility is best viewed

as a “couples problem” that results when one or more of the

conditions for fertilization isn’t met in one or both partners

(Figure 16.14A).

Fertility drugs stimulate ovulation

In about one-third of cases, infertility is traced to poor-

quality oocytes or to irregular or absent ovulation. These

situations are most common in women over the age of 37. A

couple’s first resort may be fertility drugs, in the hope that

one or more ovarian follicles will produce a healthy oocyte.

One commonly used drug, clomi-

phene, stimulates the pituitary gland

to release FSH. As noted in Section

15.3, this hormone triggers ovula-

tion. A drug called human menopausal

gonadotropin (hMG) is basically a

highly purified form of FSH. Injected

directly into the bloodstream, it stimulates ovulation in 70 to

90 percent of women who receive it.

Although fertility drugs have been used with great

success since the 1970s, they can cause undesirable side

F i g u r e 16.14 ART may allow a couple to overcome infertility. A Major causes

of infertility in females (above) and males (below). B Doctor inserting a human

sperm into an egg during in vitro fertilization. He is viewing the cell through a

microscope. The procedure is magnified on a monitor. The egg, held in place

by the tip of a pipette, is being pierced by a micromanipulator (the shadowy

line on the right). (© Cengage Learning)

16.8

Oviduct blockage

Uterine problems

Damaged or

absent ovaries 30–50%

40%

Hormone-

related

ovulation

problems

Cervical problems

≤10%

Unknown

Semen disorders

Testicular failure

Other

Obstruction

Undescended

testes

Varicocele

37%

6%

6%

7%

9%

10%

25%

© Heidi Specht, West Virginia University

A

B

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