Background: In-vitro oocyte maturation is an appealing alternative in reproductive medicine but the results obtained are still poor. The aim of our prospective and observational investigation was to study the hormonal modifications that immature follicular aspiration might induce in a natural cycle as well as the implications that these alterations may have in the endometrium.
Methods: Eleven patients (13 cycles) were included in our in-vitro oocyte maturation programme. Ovaries were scanned with transvaginal probes every day and follicular aspiration was performed when a follicle of 9 mm was visualized. Blood was also drawn for hormonal analysis. Endometrial thickness was recorded every day after oocyte retrieval. Two endometrial biopsies were taken on days 6 and 8 after oocyte retrieval.
Results: We observed a significant drop in serum oestradiol concentrations after immature oocyte retrieval previous to follicle dominance. Immediately after, rises in both FSH and LH were detected. Also, a new dominant follicle started to grow 3-4 days later. Steroid hormones secreted by this newly recruited follicle were significantly lower than in controls, inducing inadequate endometrial thickness.
Conclusions: These studies show that exogenous hormonal administration might be necessary to achieve a correct endometrial growth when in-vitro oocyte maturation is employed in IVF.