Intrauterine G-CSF Infusion for Thin Endometrium (GIFT)

Thin endometrium remains a clinical challenge in assisted reproductive technology because it may reduce endometrial receptivity and the chance of successful embryo implantation and live birth. Several treatment strategies have been used for thin endometrium, including hormonal treatment, medications to improve blood flow, endometrial stimulation, and intrauterine infusion of granulocyte colony-stimulating factor (G-CSF). However, the clinical benefit of intrauterine G-CSF infusion remains uncertain, partly because previous studies have differed in patient populations, timing of administration, dose, and study design.

This study is designed to evaluate whether intrauterine infusion of G-CSF during the endometrial preparation phase can improve reproductive outcomes in patients with thin endometrium undergoing frozen-thawed embryo transfer. The study uses a prospective, single-center, randomized, parallel-group, blinded, superiority design. Eligible participants will be randomly assigned in a 1:1 ratio to receive either mild endometrial stimulation with intrauterine G-CSF infusion or mild endometrial stimulation with intrauterine normal saline infusion. Randomization will be performed using an interactive web response system.

All participants will receive routine endometrial preparation for frozen-thawed embryo transfer according to local clinical practice. In the intervention group, participants will undergo mild endometrial stimulation followed by intrauterine infusion of G-CSF 300 μg. In the control group, participants will undergo the same mild endometrial stimulation procedure followed by intrauterine infusion of an equal volume of normal saline. Participants, outcome assessors, and statistical analysts will be blinded to group assignment, while the physician performing the intrauterine procedure will not be blinded.

After the intrauterine procedure, endometrial development will be monitored by ultrasound. Embryo transfer will be performed after endometrial transformation according to the frozen-thawed embryo transfer protocol. Participants will be followed for pregnancy outcomes, delivery outcomes, and safety events. The study aims to determine whether the addition of intrauterine G-CSF to mild endometrial stimulation provides a clinically meaningful benefit compared with mild endometrial stimulation and saline control.