Spontaneous twin pregnancy occurs in approximately 1-2 out of every 100 pregnancies. In recent decades in developed countries, the rate of twin pregnancy has increased to 3-4% due to multiple causes such as the increase in maternal age, the increase in assisted reproductive techniques, etc.
Reproductive treatments substantially increase the prevalence of twin pregnancy in our population, compared to natural conception.
Within twin gestation we can differentiate two large groups: monozygotic twins (fertilization of a single oocyte by one sperm, which divides after fertilization) and dizygotic twins (fertilization of two oocytes by two sperm).
Dizygotic twins are more common in IVF cycle gestations than in spontaneous conditions because some patients receive a double embryo transfer. IVF increases the percentage of embryo division and is also responsible for an increase in the number of monozygotic twins.
As for cycles without IVF, with ovulation inducers and artificial insemination, they also increase the percentage of dizygotic twin pregnancies because of the possibility of multiple ovulation and fertilization. This possibility can be diminished by being selective when performing our insemination protocols, trying to prioritize monofollicular development in the AI cycle.
