2.4.1. Treatment protocol.
Eligible severely infertile patients are randomly assigned (2:1 ratio) to receive immunosuppressive therapy with oral tacrolimus at a daily dose of 2 mg (low-dose group) or 4 mg (high-dose group). Randomization is based on the pre-allocated block sizes and stratified by the Th1/Th2 cell ratio (≥14.9 or <14.9) in the peripheral blood of the participants. The study drug is administered for a total of 16 days, starting 2 days before ET.