Quadruplets, far scarcer than twins or triplets, had around 3,556 sets recorded globally up to 2007. Their frequency has increased due to advances in fertility treatments, with about 70 sets of identical quadruplets existing worldwide. Various combinations of identical and fraternal siblings are common among quadruplets, including configurations like three identical siblings with one fraternal or two sets of identical twins.
An intriguing case is the Genain quadruplets, who all developed schizophrenia. In the UK, quadruplets are often colloquially referred to as “quads.” A multiple pregnancy results when a mother gives birth to more than one child, a phenomenon seen across many mammalian species, though with varying prevalence.
While in the animal kingdom, a group of newborns is sometimes called a litter, and multiple births may outnumber single ones, human multiple pregnancies are unusual. They are particularly rare among the largest mammals, marking such events as extraordinary in the realm of human childbirth.