Multi-Fetal Pregnancy

In humans [4], multi-fetal pregnancy [5] occurs when a mother carries more than one fetus [6] during the pregnancy [7]. The most common multi-fetal pregnancy [5] is twins, but mothers have given birth to up to eight children (octuplets) from a single pregnancy [7]. Multiple fetuses can result from the release of multiple eggs or multiple ovulations, the splitting of a single fertilized egg [8], or fertility treatments such as in vitro [9] fertilization [10] (IVF), which involves the insertion of many fertilized eggs into the mother?s uterus [11]. The specific ways that multiples are conceived determines the degree of relatedness between individuals within the set. The detection of multiple fetuses can be made by using ultrasound [12] technology, through hormone [13] testing, and through the discovery of multiple heart beats. Some multiple births may be deemed high-risk due to the number of fetuses, due to their arrangement, or due to complications during development.