ABSTRACT
The classically quoted rate of twinning is approximately one in every 80 pregnancies; however, this is based on delivery rates. With regular use of early ultrasounds, it has recently been realised that the rate of conception is probably much higher and in the order of one in 20. It therefore seems likely that, for every four sets of twins conceived, one or both fetuses will be lost in three cases. The loss of one of a set of twins may well be the explanation for episodes of very heavy bleeding in early pregnancy, where a clinical diagnosis of a complete miscarriage is made, yet the fetus survives. The vanishing twin may vanish completely or, if death occurs later on in pregnancy, may be retained as a semi-recognisable remnant. In its most complete form, this is known as a fetus papyraceous.
