Prenatal development

Embryo 56 Day Old Heart and Blood Vessel: Computer Generated Image from Micro-MRI, actual size of embryo = 30.0 mm - This image provides a right-sided perspective of an embryo during its eighth week of development. The age is calculated from the day of fertilization. The skin has been made translucent so that internal organs can be observed. The brain is highlighted in yellow-orange. Red blood vessels branching from the functionally complete, four-chambered heart, indicated in red, extend towards the brain. In the facial region, the red circle indicates the eye. The liver, shown in pale yellow, is situated below the heart.

Prenatal development is the process in which an embryo and later fetus develops during gestation. Prenatal development starts with fertilization the first stage in embryogenesis which continues in fetal development until birth.

In human pregnancy, prenatal development, also known as antenatal development, is the development of the embryo following fertilization, and continued as fetal development. By the end of the tenth week of gestational age the embryo has acquired its basic form and is referred to as a fetus. The next period is that of fetal development where many organs become fully developed. This fetal period is described both topically (by organ) and chronologically (by time) with major occurrences being listed by gestational age.

In other animals the very early stages of embryogenesis are the same as those in humans. In later stages, development across all taxa of animals and the length of gestation vary.

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