ABSTRACT
Monozygotic (MZ) twinning represents a relatively rare form of multiple gestation. The incidence of spontaneous MZ twinning (i.e. twins which originate from a single embryo) in humans is relatively stable3, and the medical risks associated with MZ twins are highly dependent upon whether the twins are contained within a single chorion or amnion – a phenomenon that is dictated by the timing of embryo splitting3,4 (see Chapters 24 and 28). As expected, monochorionic and monoamniotic twins have a higher risk of exhibiting fetal abnormalities than diamniotic/dichorionic MZ twins. MZ twinning can be experimentally induced by tampering with the zona pellucida, either via chemical or mechanical methods3. Such observations preceded speculations that MZ twinning can be increased following ART5.
