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Prenatal development (from Latin natalis 'relating to birth') involves the development of the embryo and of the fetus during a viviparous animal's gestation.Prenatal development starts with fertilization, in the germinal stage of embryonic development, and continues in fetal development until birth.
Nine-week-old human embryo from an ectopic pregnancy. Organogenesis is the development of the organs that begins during the third to eighth week, and continues until birth. Sometimes full development, as in the lungs, continues after birth. Different organs take part in the development of the many organ systems of the body.
A fetus or foetus (/ ˈ f iː t ə s /; pl.: fetuses, foetuses, rarely feti or foeti) is the unborn mammalian offspring that develops from an embryo. [1] Following the embryonic stage, the fetal stage of development takes place.
Fetal heart tone (the sound of the heart beat) can be heard using doppler. Nipples and hair follicles begin to form. Location of the elbows and toes are visible. Spontaneous limb movements may be detected by ultrasound. All essential organs have at least begun. The vitelline duct normally closes.
The fetal circulation is composed of the placenta, umbilical blood vessels encapsulated by the umbilical cord, heart and systemic blood vessels. A major difference between the fetal circulation and postnatal circulation is that the lungs are not used during the fetal stage resulting in the presence of shunts to move oxygenated blood and ...
Fertilization is the event most commonly used to mark the beginning point of life, in descriptions of prenatal development of the embryo or fetus. [28] The resultant age is known as fertilization age, fertilizational age, conceptional age, embryonic age, fetal age or (intrauterine) developmental (IUD) [29] age.
Human pregnancy can be divided into three trimesters, each approximately three months long: the first, second, and third trimester. The first trimester is from the last menstrual period through the 13th week, the second trimester is 14th–28/29th week, and the third trimester is 29/30th–42nd week. [ 6 ]
In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. [2] [4] The main stages of animal embryonic development are as follows: The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula.