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fertilization
(fur´tĭ-lĭ-za´shәn)
in human reproduction, the process by which the male's sperm unites with the female's oocyte, creating a new life. The sex and other biologic traits of the new individual are determined by the combined genes and chromosomes
that exist in the sperm and oocyte. See also conception and reproduction. Called also fecundation and impregnation. After injection into the vagina, millions of sperm cells (spermatozoa) make use of their whiplike tails to swim through the cervix toward the uterus. Most are destroyed along the way by secretions
in the vagina, but some reach the uterus and a few may enter the fallopian tubes. A very small number may survive as long as 48 hours. If during this period only one sperm succeeds in entering a fallopian
tube and meeting there an oocyte ready to be fertilized, conception can occur. This event is possible only during a period
of about 4 days of the month. After the sperm lodges in the oocyte, the tail disappears, but the head unites with the oocyte
to form the zygote.
in vitro fertilization
the process by which conception takes place in a laboratory medium. A lay term for the product of in vitro fertilization is “test tube baby.”The treatment cycle involves the following steps: (1) Induction of ovulation with fertility drugs, such as clomiphene citrate or injectable follicle-stimulating hormone and luteinizing hormone (either separately or in combination), to produce multiple ovarian follicles. When the largest follicle reaches 20 mm in diameter the patient is given an injection of human chorionic gonadotropin to
induce expulsion of the oocyte from the follicle. (2) laparoscopy and follicular aspiration for the harvesting of oocytes. (3) Maturation of retrieved oocytes and inoculation with the husband's or donor's sperm. (4) incubation of the resulting embryos until they reach the two- to six-cell stage. (5) Transfer of an embryo via catheter into the patient's uterus. At this point intensive intervention ceases, the pregnancy is considered normal, and no further manipulation is required.
in vivo fertilization
union of the sperm and oocyte within the reproductive tract of the female; usually referring to those types of artificial insemination in which the sperm is artificially introduced into the vagina, cervix, or uterine cavity.
Copyright 2007. An Elsevier publication. All rights reserved.
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