Karimzadeh 2012.

Methods	Single‐centre, 2‐arm, parallel RCT
Participants	70 women undergoing FET Inclusion criteria: not stated Exclusion criteria: not stated Baseline demographic and infertility characteristics similar in both groups
Interventions	Natural cycle (36 women) Women did not receive any HT. When mature follicle reached a mean diameter of 18 mm and endometrial thickness > 8 mm, HCG 10,000 IU administrated and FET was done 4 days after HCG injection HT (34 women) Women received oral estradiol valerate 6 mg/d from day 2 of menstrual cycle and progesterone 100 mg IM in oil. When endometrial thickness reached > 8 mm, FET was done 72 hours after beginning of progesterone administration, and estradiol and progesterone were continued until the 12th gestational week
Outcomes	Miscarriage per ET Ongoing pregnancy per ET Clinical pregnancy per ET
Notes	Data reported as per 'embryo transfer' and number of embryos transferred was not equivalent to the number of women randomized
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Not reported but non‐blinding of outcome assessors may not have affected some of the outcome measures as they were objectively assessed.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Proportions of withdrawals/losses to follow‐up and reasons for withdrawal not reported; analysis was per ET
Selective reporting (reporting bias)	Unclear risk	Insufficient information to make a conclusive judgement
Other bias	Low risk	Baseline demographic and infertility characteristics similar in both groups