Monozygotic multiple pregnancies following IVF: a case report series of rare experience

Monozygotic multiple pregnancies are three times more common after assisted reproduction (with or without IVF) than after spontaneous conception (1.2% versus 0.4%). These pregnancies are associated with multiple maternal and fetal risks. This article is a description of nine cases of monozygotic pregnancies following IVF at the OVO Clinic (Montreal) between January 2007 and August 2011 and a scientific review of the literature on monozygotic multiple pregnancies after assisted reproductive treatment found in the MEDLINE and Cochrane Databases. In this retrospective series, 3522 embryos were transferred and 1033 pregnancies were obtained, of which there were nine monozygotics (0.87%). The exact mechanism behind this increased frequency remains uncertain. Possible explanations associated with fertility treatments include alterations of the zona pellucida, transfers at the blastocyst stage, prolonged culture, preimplantation genetic diagnosis, ovarian stimulation and maternal age. Assisted reproduction treatment appears to increase monozygotic pregnancies; however, the rate is still low and therefore it is difficult to exactly conclude the real mechanism.There are two types of multiple pregnancy: the dizygotic (two different embryos) and the monozygotic (one embryo which splits to make two identical genetic embryos). We know the risk factors for dizygotic pregnancies, but the mechanism of monozygotic pregnancies remains unclear. Assisted reproduction treatment seems to increase the multiple monozygotic pregnancy rate to 3-times more than that in nature. Several possibilities could be suspected as responsible for these monozygotic multiple pregnancies – advanced maternal age, alterations of the zona pellucida, transfers at the blastocyst stage, prolonged culture and ovarian stimulation – but a absolute explanation is not yet defined. This article is a scientific review of the literature on monozygotic multiple pregnancies after IVF treatment and a description of nine cases following IVF treatment at the OVO Clinic in Montreal between January 2007 and August 2011. The bibliographic references were found in the Medline and Cochrane Database.