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