Endometrial Thickness Management in FET Cycle on Day 4
Your endometrium at 9.4 mm on day 4 of Progynova is already adequate—continue your current Progynova regimen without modification and proceed with standard monitoring until progesterone initiation. 1, 2
Why Your Current Thickness is Favorable
An endometrial thickness of 9.4 mm on day 4 exceeds the threshold associated with optimal outcomes. Research demonstrates that endometrial thickness ≥8 mm is considered adequate for FET cycles, with pregnancy rates improving as thickness increases beyond this cutoff 1, 2
The critical threshold of 8.75 mm for predicting live birth has already been surpassed in your case. A large retrospective study of 1,512 IVF cycles identified this specific cutoff, with clinical pregnancy rates ranging from 50% at ≤6 mm to 84.2% at >16 mm 2
Your endometrium will continue to thicken with ongoing Progynova administration. Studies show endometrial development progresses throughout the estrogen supplementation phase, and your current measurement suggests excellent response 3
Standard Protocol to Follow
Continue your current Progynova dose without adjustment. There is no evidence supporting dose escalation when endometrial thickness already exceeds 8 mm 4, 3
Schedule your next ultrasound monitoring according to your clinic's standard protocol (typically around day 10-14 of estrogen supplementation) to confirm continued adequate thickness before progesterone initiation 4
Plan to initiate progesterone supplementation when your endometrium reaches your clinic's target thickness (typically 7-8 mm minimum, which you've already achieved) and appropriate duration of estrogen priming is complete 4
Key Clinical Context
Endometrial thickness in fresh cycles predicts FET cycle thickness better than the FET measurement itself. If you had adequate thickness in a previous fresh cycle, this further supports your favorable prognosis 1, 2
The specific formulation and route of progesterone supplementation (intramuscular, vaginal, or oral) shows comparable outcomes, so follow your clinic's standard protocol 4
Additional interventions like transdermal estrogen or vaginal Femoston are reserved for patients with inadequate thickness (<7-8 mm), which does not apply to your situation 5, 3
Common Pitfall to Avoid
Do not add additional estrogen supplementation or modify your protocol based on this measurement. Your thickness is already in the optimal range, and unnecessary intervention could disrupt the carefully timed endometrial preparation without improving outcomes 3