Prenatal development

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. The term "prenate" is used to describe an unborn offspring at any stage of gestation.

In humanpregnancy, prenatal development is also called antenatal development. The development of the human embryo follows fertilization, and continues 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.

The very early stages of embryonic development are much more similar across mammals, though development rate differs quite a bit; this is also the case within human populations (Which makes the temporal discussion of what a zygote, embryo or fetus is like only an approximation based upon some sample). The longer the gestation the more time for divergence and spread in estimates occur. Which is thus also much more the case across different mammals. Also the length of gestation varies greatly. Some mammals favor releasing their offspring into the world much earlier, presenting the offspring with much greater risk and worse development. Though lower risk to the mother. It is a trade off between offspring and maternal safety. Humans 9 and elephants (22) have an extreme variety with very few offspring and very long gestation time. As opposed to oppossums going as low as 11 days before birth.