Endometrial dating chart
On the contrary, hormone replacement cycle with exogenous estradiol (E2) administration is recommended for older women, those without ovaries or with irregular menstrual cycles.
This protocol is also preferred when we want to synchronize the time of ET for the needs of the patient or of the IVF center (35).
Surgeries, such as reiterated curettage intracavitary myomectomy and polypectomy may lead to intrauterine adhesions and damage the endometrium via the same mechanism (23).
Various strategies have been studied over the years to try to increase the endometrial thickness in poor endometrial responders (Figure 1): among the others, those currently considered in the clinical practice are the extended use of exogenous estrogens (24), the administration of low-dose Aspirin (25), Tocopherol (in association with Pentoxifylline) (26, 27), vaginal Sildenafil Citrate (28), Electroacupuncture (29) and application of Granulocyte Colony Stimulation Factor (G-CSF) (30).
Recently, thanks to the scientific progress in molecular biology, genetics and metabolomics, the implantation process is becoming increasingly clear and these new research tools could soon provide innovative solutions to improve outcomes.
In women in which the endometrium does not grow under the standard E2 regimen (10–12 days of daily administration), the extended use of exogenous estrogens consists in the administration of estradiol at a higher dose and for a period of time longer than the one sufficient for conventional therapy. (24), among 36 women enrolled, 23 were subjected to a fresh embryo transfer (control group), while 13 were suggested to cancel it, because of poor response, and become part of the study group.
These women were then subjected to a frozen-thawed embryo transfer in the next cycle after extended exogenous estrogen replacement.
Physiologically, the endometrium responds to hormonal influence according to the Noyes criteria (transition from proliferative to secretory and menstrual phases) (34).
In clinical practice, advances in embryo culture technology and cryopreservation programs have determined an increase frozen-thawed blastocyst stage transfer.