Hum Reprod. 2001 Jul;16(7):1518-26. doi: 10.1093/humrep/16.7.1518.
Developed countries have experienced both some population growth and unprecedented declines in fertility rates during the last half of the twentieth century. Couples now have fewer than two children on average in most European countries and they tend to postpone these births until a later age. A decline in male fertility has been suggested by some studies of semen quality, but there is contrasting evidence of shorter times to pregnancy for couples trying to conceive. An important economic factor is the income of young men relative to their parents' incomes, which determines how they rate the ability of their own earnings to support a family. Lower relative income in the 1970s was associated with a lower fertility rate. The decline in fertility in the USA may have been attenuated by the sharp rise in female income during the late 1960s and early 1970s, allowing women to take advantage of purchased child care, thus maintaining the relative family income. The level of demand for children does not appear to be set by known psychological factors, although explanations for the desire to reproduce have been sought in biological, psychoanalytical and socio-cultural research. Recent studies indicate that adults with secure attachment relationships are more interested in being parents. Possible epidemiological factors include age at first marriage, but in Eastern Europe, where age at first marriage is as low as 22 years, fecundity rates do not exceed 1.5. When mothers' age cohorts are analysed, the mean fecundity rate has been falling since the 1920s. Health factors affecting population trends include the change in contraceptive prevalence over the last 40 years. The prevalence of sub-fertility remains close to 10%, and studies from a number of countries indicate that approximately 50% of infertile couples make use of infertility services including IVF and intracytoplasmic sperm injection which are available in 45 countries covering 78% of the world's population. It is estimated that the level of service is sufficient for less than one-third of the need.
在20世纪后半叶，发达国家经历了人口增长以及生育率前所未有的下降。在大多数欧洲国家，如今夫妇平均生育子女数不足两个，而且他们往往会推迟生育，直到年龄更大的时候。一些关于精液质量的研究表明男性生育能力有所下降，但也有相反的证据显示，尝试受孕的夫妇怀孕所需时间缩短。一个重要的经济因素是年轻男性相对于其父母收入的情况，这决定了他们对自己收入支撑家庭能力的评估。20世纪70年代相对收入较低与较低的生育率相关。美国生育率的下降可能因20世纪60年代末和70年代初女性收入的急剧上升而有所缓和，这使得女性能够利用购买的儿童保育服务，从而维持家庭相对收入。对孩子的需求水平似乎并非由已知的心理因素决定，尽管人们在生物学、精神分析学和社会文化研究中寻找生育愿望的解释。最近的研究表明，具有安全依恋关系的成年人对为人父母更感兴趣。可能的流行病学因素包括初婚年龄，但在东欧，初婚年龄低至22岁，生育率不超过1.5。当分析母亲的年龄组时，自20世纪20年代以来平均生育率一直在下降。影响人口趋势的健康因素包括过去40年避孕普及率的变化。亚生育力的患病率仍接近10%，多个国家的研究表明，约50%的不孕夫妇利用不孕不育服务，包括体外受精和胞浆内单精子注射，这些服务在覆盖世界78%人口的45个国家可用。据估计，服务水平仅能满足不到三分之一的需求。
