Introduction:
It has been over 40 years since the development of assisted reproductive technology. With the improvements of assisted reproductive technologies such as ovulation induction, embryo culture and vitrification, and other technologies, experts in the field of reproductive medicine are no longer only concerned about pregnancy rates, but of delivering healthy live births. At present, the most common clinical transfer strategies include twin embryo and single blastocyst transfer. In addition, single embryo and double blastocyst transfer will also be performed in the clinic under certain conditions. How to choose a way that can ensure the success rate of transplantation and reduce the incidence of complications to the greatest extent is the focus of clinicians. Different transplantation methods may have different outcomes in different countries and races1, 2. In order to study the advantages and disadvantages of these four transplantation methods, we selected two large reproductive medical centers, one in Beijing and the other in Shenzhen, to represent the northern and southern regions of China respectively. The majority of individuals in China belong to the Mongoloid race. This study aims to provide an evidence-based assessment of the benefits and harms of four transplantation methods so as to improve the superior pregnancy outcome and reduce the pregnancy rate of multiple embryos in the Mongoloid race.