Randomization, intervention, and blinding
The enrolled patients were randomized (1:1) on the day of receiving their hysteroscopy, in which 39 were randomized to the transdermal estrogen gel group and 39 to the estradiol valerate tablet (oral) group. The random number list was generated by using SPSS software (Version 19.0; SPSS Inc, IL). The investigators were blinded to the treatment allotment. Based on the pharmacokinetics data provided by the manufacturer of each drug, the transdermal estrogen gel contains 0.06% 17-beta estradiol (Jianmin Group Pharmaceutical Co. Ltd, China), that is 1.5 mg estradiol in 2.5 g gel. We chose 10 g of estradiol gel (containing 6 mg of 17-beta estradiol) to compare with 6 mg of estradiol valerate. The treatment group received 5 g twice daily of transdermal estrogen gel, and the control group received oral treatment with 3mg twice daily of estradiol valerate (Progynova, Bayer). All subjects received hormone treatment for two cycles.