fetusembryology also spelled foetus
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![Human fetus, pen and ink studies by Leonardo da Vinci, c. 1510.[Credits : The Granger Collection, New York]](http://media-2.web.britannica.com/eb-media/57/8557-003-E2E105BD.gif "Human fetus, pen and ink studies by Leonardo da Vinci, c. 1510.[Credits : The Granger Collection, New York]")
the unborn young of any vertebrate animal, particularly of a mammal, after it has attained the basic form and structure typical of its kind.
A brief treatment of the fetus follows. For more information on the human fetus, see pregnancy.
Biologists arbitrarily speak of the earliest stages of development of the fertilized egg as the embryonic period, which ends when the external form of the embryo begins to resemble clearly the newborn of the group to which it belongs. The next period, culminating in birth, is the fetal period. In human development this transition occurs in approximately the eighth week after conception. The fetal stage is characterized by increased growth and by the full development of the organ systems.
Some fetal disorders may cause birth of the infant before term. If spontaneous expulsion occurs before the human fetus has reached a stage of development advanced enough to allow it to live outside the womb (20 to 22 weeks), it is spoken of as an abortion or, commonly, a miscarriage. Expulsion of a dead fetus thereafter is considered a stillbirth and of a living fetus a premature birth. Postmature birth is one occurring more than three weeks beyond the expected date of delivery.
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Table of Contents
Media
- Human fetus, pen and ink studies by Leonardo da Vinci, c. 1510.[Credits : The Granger Collection, New York]
- Development of the human embryo. Embryo of six weeks (N) within halved amnion, chorion, and …[Credits : Encyclopædia Britannica, Inc.]
- After fertilization, the embryo travels along the fallopian tube to the uterus, where it will grow.[Credits : Encyclopædia Britannica, Inc.]
- When a woman is pregnant, there is no such thing as drinking a safe amount of alcohol.[Credits : Acquired from Vast Video]
- When a pregnant woman uses drugs or alcohol, her baby does too.[Credits : Acquired from Vast Video]
- A mother’s drug or alcohol use can affect an unborn baby during each of the three trimesters of …[Credits : Acquired from Vast Video]
- Smoking cigarettes or marijuana during pregnancy can cause serious problems for your baby.[Credits : Acquired from Vast Video]
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