The modified extra-long protocol can effectively improve endometrial tolerance—higher clinical pregnancy rate in patients with recurrent fertilization failure The modified extra-long protocol has been applied in our center for the past 2 years to treat recurrent IVF cycle fertilization failure cases with good results. We have treated many cases of multiple failed IVF cycles in our center, and one fresh embryo transfer was successful after the modified extra-long protocol, and up to now, the clinical pregnancy rate of fresh embryo transfer with the modified extra-long protocol in our center can reach 65%-70%.