In this report we present an unusual case of a couple who achieved a twin pregnancy by intracytoplasmic sperm injection (ICSI) with a single immature oocyte retrieved. The oocyte was at metaphase I at 39 h post human chorionic gonadotrophin (hCG) administration, which is our standard ICSI time. Extended culture allowed the extrusion of the polar body, and sperm injection was performed at 43 h post-trigger. The fertilized egg underwent embryo biopsy on day 3 and preimplantation genetic assessment for three chromosomes (X, Y and 21). The embryo remained in culture until day 5. Later, the biopsy results reported a transferable embryo, which was replaced to the uterine cavity at blastocyst stage. Pregnancy test gave a positive β-hCG result, and the 6 weeks’ scan, performed to confirm the fetal heart, revealed the presence of one amniotic sac and two fetal heartbeats, which currently have been so far eventless and smooth, ongoing at 18 weeks of gestation.