Final answer:
The incidence of spontaneous dizygotic twinning is about 1 in 125 pregnancies. This rate increases with a family history of twinning and is even higher when using ART, due to the possibility of transferring multiple embryos to the uterus.
Step-by-step explanation:
The question pertains to the incidence of spontaneous dizygotic twinning, dizygotic twinning with a family history, and the incidence of dizygotic twinning with the use of Assisted Reproductive Technologies (ART). Normally, during an ovulation cycle, a woman typically releases a single egg. However, in approximately 1 percent of ovulation cycles, two eggs may be released and subsequently fertilized, leading to the birth of dizygotic twins. Dizygotic twins come from two separate eggs and sperm and are no more genetically identical than siblings born at different times.
Familial history can increase the probability of dizygotic twinning, as can the use of ART, which includes techniques such as in vitro fertilization (IVF). ART significantly boosts the likelihood of multiple births because more than one embryo may be transferred into the uterus to increase the chances of a successful pregnancy.
Therefore, the incidence rates of dizygotic twinning are important to understand as they vary from natural conception to cases with a family history of twins, and especially when ART is involved, where the rates are considerably higher.