Triplet pregnancy in a cynomolgus monkey (Macaca fascicularis) after double embryo transfer

At our research center, cynomolgus monkeys (Macaca fascicularis) are bred by mating or intracytoplasmic sperm injection (ICSI) and embryo transfer. We typically transfer 2 embryos, because the pregnancy rate is better than that for single embryo transfer. In the case we present here, 2 embryos that had been frozen and thawed after ICSI were transplanted into a recipient female macaque, and a multiple pregnancy (3 fetuses) was confirmed. All 3 fetuses were miscarried between days 81 and 85 of pregnancy. One fetus, which was wrapped in the amnion, was expelled along with its own placenta and one other. Because the other placenta had 2 umbilical arteries, 2 fetuses may have shared it. Therefore, we believe this pregnancy was a case of triplets, including a set of twins from an embryo that divided after transfer.