In the early years of in vitro fertilization, overall pregnancy rates were low, and it was considered necessary to transfer more than one embryo to increase the chances of pregnancy. It was not until advances in assisted reproductive technologies resulting in increased pregnancy rates that the concept of transferring just one embryo was considered possible. A consequence of improvements in implantation rates was also an increase in multiple pregnancies when more than one embryo was transferred. Although some countries have reduced the number of embryos transferred, international data show that in many parts of the world high twin and higher order multiple pregnancy rates still exist. Even in developed countries these problems persist depending on clinical practice, funding of health services, and patient demands. Perinatal and other outcomes are significantly worse with twins compared with singleton pregnancies and there is an urgent need to reduce multiple pregnancy rates to at least 10%. This has been achieved in several countries and clinics by introducing single embryo transfer but there are many barriers to the introduction of this technique in most clinics worldwide. We discuss the background to the high multiple rate in assisted reproduction and the factors that contribute to its persistence even in excellent clinics and in high-quality health services. Practices that may promote single embryo transfer are discussed.

中文翻译：

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为什么全球多胎妊娠率和单胚胎移植率如此不同，我们该怎么办？

在体外受精的早期，整体受孕率较低，认为需要移植一个以上的胚胎以增加受孕机会。直到辅助生殖技术的进步导致怀孕率增加，仅移植一个胚胎的概念才被认为是可能的。植入率提高的一个结果是，当移植一个以上的胚胎时，多胎妊娠的几率也会增加。尽管一些国家减少了移植胚胎的数量，但国际数据显示，在世界许多地方，高双胎和高阶多胎妊娠率仍然存在。即使在发达国家，这些问题仍然存在，这取决于临床实践、卫生服务资金和患者需求。与单胎妊娠相比，双胞胎的围产期和其他结局明显更差，因此迫切需要将多胎妊娠率降低至至少 10%。这已在多个国家和诊所通过引入单胚胎移植实现，但在全球大多数诊所引入该技术存在许多障碍。我们讨论了辅助生殖高倍率的背景，以及即使在优秀的诊所和高质量的医疗服务中也能持续存在的因素。讨论了可能促进单胚胎移植的做法。这已在多个国家和诊所通过引入单胚胎移植实现，但在全球大多数诊所引入该技术存在许多障碍。我们讨论了辅助生殖高倍率的背景，以及即使在优秀的诊所和高质量的医疗服务中也能持续存在的因素。讨论了可能促进单胚胎移植的做法。这已在多个国家和诊所通过引入单胚胎移植实现，但在全球大多数诊所引入该技术存在许多障碍。我们讨论了辅助生殖高倍率的背景，以及即使在优秀的诊所和高质量的医疗服务中也能持续存在的因素。讨论了可能促进单胚胎移植的做法。