Transnational gamete donation (TGD) programme: What is the optimal number of oocytes to be allocated?

To assess the most adequate number of oocytes that allows the maximum live birth rate with the least number of residual vitrified embryos in a TGD programme.

A retro-prospective observational study was conducted in the Centre for Assisted Reproduction of the University hospital of Careggi, Florence. Vitrified oocytes were shipped from two biobanks. In the receiving centre, gametes were warmed, inseminated and the subsequent embryo transfer was performed. The recipients' cohort was divided according to numbers of received oocytes (Groups A:3; B: 6; C:8 oocytes). Conservative and optimal estimates of the cumulative live birth rate (CLBR) were calculated per warming cycle. The proportion of babies born for every oocyte (oocyte-to-baby rate) and the number of supernumerary embryos for each newborn was also calculated in different subgroups.

Six hundred forty-five oocyte donors' cycles were included: 18 in group A, 580 in group B, 47 in group C. CLBR in group C was 41.5 % and showed higher than group A (17.6 %) but similar to group B (33.6 %). A higher number of embryos were vitrified in group B and C when compared to A (40.4 %, 32.4 % and 4 % respectively, P < 0.05). All indicators on the evaluation of supernumerary embryos show a linear relation with the number of consumed oocytes but vitrified embryos in 'patients not achieving at least one LB' were similar between group B and group C.

These data indicate that the most adequate number of oocytes in a TGD context, appears to be six. Eight oocytes increase live birth rate but not significantly and increase number of residual embryos without increasing success rate in patients not achieving at least one live birth.