8.7 Multiple pregnancy
In this section, we turn to the subject of multiple pregnancy, when there is more than one fetus in the uterus. More than 95% of multiple pregnancies are twins (two fetuses), but there can also be triplets (three fetuses), quadruplets (four fetuses), quintuplets (five fetuses), and other higher order multiples with a declining chance of occurrence. The spontaneous occurrence of twins varies by country: it is lowest in East Asian countries like Japan and China (1 out of 1000 pregnancies are fraternal or non-identical twins), and highest in black Africans, particularly in Nigeria, where 1 in 20 pregnancies are fraternal twins. In general, compared to single babies, multiple pregnancies are highly associated with early pregnancy loss and high perinatal mortality, mainly due to prematurity.