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Advanced maternal age, in a broad sense, is the instance of a woman being of an older age at a stage of reproduction, although there are various definitions of specific age and stage of reproduction.〔(Effect of advanced age on fertility and pregnancy in women ) at UpToDate. Author: Ruth C Fretts. Section Editor: Louise Wilkins-Haug. Deputy Editor: Vanessa A Barss. This topic last updated: Dec 3, 2012.〕 The variability in definitions regarding age is in part explained by the effects of increasing age occurring as a continuum rather than as a threshold effect.〔 In Western, Northern, and Southern Europe, first-time mothers are on average 26 to 29 years old, up from 23 to 25 years at the start of the 1970s. In a number of European countries (Spain), the mean age of women at first childbirth has now even crossed the 30 year threshold.〔http://www.oecd.org/els/soc/SF2.3%20Mean%20age%20of%20mother%20at%20first%20childbirth%20-%20updated%20240212.pdf〕 This process is not restricted to Europe. Asia, Japan and the United States are all seeing average age at first birth on the rise, and increasingly the process is spreading to countries in the developing world like China, Turkey and Iran. In the U.S., the average age of first childbirth was 26 in 2013.〔http://www.cdc.gov/nchs/fastats/births.htm〕 In present generations it is more common to have children at an older age. Several factors may influence the decisions of mothers when having their first baby. Such factors include educational, social and (probably the most important) economic status. ==History== Having children later was not exceptional in the past, when families were larger and women often continued bearing children until the end of their reproductive age. What is so radical about this recent transformation is that it is the age at which women give birth to their first child which is becoming comparatively high, leaving an ever more constricted window of biological opportunity for second and subsequent children, should they be desired. Unsurprisingly, high first-birth ages and high rates of birth postponement are associated with the arrival of low, and lowest-low fertility. This association has now become especially clear, since the postponement of first births in a number of countries has now continued unabated for more than three decades, and has become one of the most prominent characteristics of fertility patterns in developed societies. A variety of authors (in particular Lesthaeghe) have argued that fertility postponement constitutes the ‘hallmark’ of what has become known as the second demographic transition. Others have proposed that the postponement process itself constitutes a separate 'third transition'. On this latter view, modern developed societies exhibit a kind of dual fertility regime, with the majority of births being concentrated either among very young or increasingly older mothers. This is sometimes known as the 'rectangularisation' of fertility patterns. 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「advanced maternal age」の詳細全文を読む スポンサード リンク
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