The efficacy and safety of endometrial preparation regimens remain controversial. In the most recent meta-analysis, using natural and modified natural cycle protocol to prepare the endometrium in frozen embryo transfer resulted in higher live birth rates. In addition, the natural cycle reduces the risk of gestational hypertension, postpartum haemorrhage, and extremely preterm delivery compared with regimens using exogenous hormones. Because there are many physiological and endocrinal differences in the frozen embryo transfer cycle with different endometrial preparation protocols, the development of children born from these regimens has received much attention. For example, there is a complete absence of the corpus luteum during the cycle of exogenous hormone administration. Or in the modified natural cycle, the pharmacokinetics is not entirely the same as the natural physiology when using an additional ovulatory injection with hCG. To date, there have been no longitudinal follow-up studies that evaluated and compared the long-term development of IVF/ICSI children born from frozen embryo transfer with different endometrial preparation protocols. Thus, the investigators conduct a follow-up of our RCT to investigate the IVF/ICSI children born from frozen embryo transfer with different endometrial preparation protocols to give strong evidence about the safety of the three most common endometrial preparation protocols in women undergoing frozen embryo transfer.