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Prenatal development
Prenatal or antenatal development is the process in which a human embryo or fetus (or ''foetus'') gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense. After fertilization, the process of embryogenesis (the early stages of prenatal development) begins. By the end of the tenth week of gestational age the embryo has acquired its basic form and the next period is that of fetal development where the 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. ==Definitions of periods==
* The perinatal period (from Greek ''peri'', "about, around" and Latin ''nasci'' "to be born") is "around the time of birth". In developed countries and at facilities where expert neonatal care is available, it is considered from 22 completed weeks (154 days) of gestation (the time when birth weight is normally 500 g) to 7 completed days after birth.〔(Definitions and Indicators in Family Planning. Maternal & Child Health and Reproductive Health. ) By European Regional Office, World Health Organization. Revised March 1999 & January 2001. In turn citing: WHO Geneva, WHA20.19, WHA43.27, Article 23〕 In many developing countries, the starting point of this period is considered 28 completed weeks of gestation (or weight more than 1000 g).〔Singh, Meharban (2010). Care of the Newborn. p. 7. Edition 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Prenatal development」の詳細全文を読む
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