Optimizing the number of embryos to transfer on day 5: two should be the limit.
To define the appropriate number of embryos to be transferred at day 5.



Retrospective analysis of 784 consecutive fresh day-5 embryo transfers performed between 2007 and 2015, divided in three groups: Group A (N = 219): received the only 2 embryos that reached a transferable stage; Group B (N = 357): received 2 selected embryos among several that reached a transferable stage; Group C (N = 208): received the only 3 developing embryos. Clinical pregnancy, implantation, multiple pregnancy and delivery rates were registered. Kruskal-Wallis and Fisher Exact tests were applied as appropriate.



Age and previous attempts were comparable in the 3 groups. Compared with Group A, Groups B and C had a higher oocyte recovery (10.7 ± 5.6 vs. 14.7 ± 8.0 vs. 13.8 ± 6.6), fertilization rate (75.97% vs. 81.60% vs. 83.29%) and percentage of embryos reaching a transferable stage on day 5 (39.98% vs. 63.99% vs. 60.97%), as well as a significantly higher clinical pregnancy (42.92% vs. 61.06% vs. 58.17%) and implantation rates (21.09% vs. 40.98% vs. 36.97%). The multiple pregnancy rate was higher in Groups B and C than in Group A (11.70% vs. 31.19% vs. 37.19%). The high order multiple pregnancy rate (> 2) was significantly increased in group C (1.06% vs. 0.92% vs. 14.05%).



In patients with 3 or more day 5 developing embryos, delivery rates are similar if 2 or 3 embryos are transferred. The transfer of 3 embryos carries an unacceptable increase in the risk of high order multiple pregnancy, with its known consequences. According to our data, we should not exceed the number of 2 day-5 fresh embryos transferred.
Fertilidad San Isidro, Buenos Aires, Argentina.
Claudio
C
Ruhlmann
Fertilidad San Isidro, Buenos Aires, Argentina.
Lucas
L
Molina
Fertilidad San Isidro, Buenos Aires, Argentina.
Graciano
G
Tessari
Fertilidad San Isidro, Buenos Aires, Argentina.
Felicitas
F
Ruhlmann
Fertilidad San Isidro, Buenos Aires, Argentina.
Lautaro
L
Tessari
Fertilidad San Isidro, Buenos Aires, Argentina.
Diego
D
Gnocchi
Fertilidad San Isidro, Buenos Aires, Argentina.
Antonio
A
Cattaneo
Fertilidad San Isidro, Buenos Aires, Argentina.
Marcela
M
Irigoyen
Fertilidad San Isidro, Buenos Aires, Argentina.
Alejandro Gustavo
AG
Martínez
D000328:Adult; D004624:Embryo Transfer / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology / Q000517:prevention & control; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D012189:Retrospective Studies
Day-5 embryo transfer; blastocyst; implantation rate; multiple pregnancies