Image Caption : Human Embryonic and Fetal Development : Three-dimensional visualization reconstructed from scanned human data of a 8 cell zygote, a 14-16 day old embryo, a 44 day old embryo, and a 9 week old fetus. The body does not increase greatly in size during the embryonic period. But during the the fetal period, beginning at week nine, a phase of rapid growth starts that continues until after birth.
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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