Hello and welcome to healthcare magic. The success of in vitro fertilisation (ivf) does not solely depend on endometrial thickness. Failure of past attempts in ivf should not deter you from taking another try (second in your case). The endometrial thickness you have mentioned is adequate for implantation and pregnancy if your doctor decides to go ahead with frozen embryo transfer. I would like to have few more details , like your age, results of your infertility work up etc before giving a more detailed answer. Hope I have answered your question to your satisfaction. Please do right back if you have any more questions. Best of luck for your second IVF attempt.