NCT02197208.

Trial name or title	A randomized controlled comparison of spontaneous natural cycles and human chorionic gonadotrophin‐induced natural cycles in frozen‐thawed embryos transfer
Methods	Randomised Parallel assignment Single‐blind (outcomes assessor)
Participants	300 women aged 19‐43 years Regular menstrual cycles ranging from 21‐35 days with not more than 4 days variation between cycles Undergoing FET in natural cycles Normal uterine cavity as shown on saline sonogram performed before the IVF cycle or normal uterine cavity shown on pelvic scanning during the stimulated IVF cycle Endometrial thickness ≥ 8 mm in both stimulated IVF and FET cycles
Interventions	Daily monitoring of LH and E2 vs HCG‐induced natural cycle
Outcomes	Primary: ongoing pregnancy rate (defined as the number of viable pregnancies beyond 10‐12 weeks' gestation per transfer cycle) Secondary: days of monitoring for timing FET; endometrial thickness on day of HCG or the next day after LH surge; implantation rate; pregnancy rate; clinical pregnancy rate; miscarriage rate; multiple pregnancy rate
Starting date	October 2014, last data collection date December 2015
Contact information	Vivian CY Lee, University of Hong Kong
Notes	No email address provided